Lake Overview and Current Condition

Yankee Lake is a 410-acre private lake in Sullivan County, New York, with a shallow maximum depth of about 12 feet (~4 meters). The submerged area of the original Yankee Pond may have a depth to about 40 feet. The Citizens Statewide Lake Assessment Program (CSLAP) is a volunteer lake monitoring program directed by the New York State Department of Environmental Conservation (NYS DEC) in collaboration with the New York State Federation of Lake Associations (NYSFOLA). The Yankee Lake Preservation Association, Inc. has been a member of NYSFOLA and participated in CSLAP for most of the past 20 years. (CSLAP did not collect or analyze data during the Covid summers of 2020 and 2021.) The analysis in this report is based on an AI analysis of the 1,730 CSLAP data points collected from Yankee Lake waters from 2005 to 2024, but with special emphasis on 2019 through 2024.

Lakes are usually classified as being in one of three possible classes: Oligotrophic, Mesotrophic, or Eutrophic, depending upon clarity, depth of light penetration, concentration of chemical ions such as phosphorus, microscopic plant life containing chlorophyll, and a host of other factors. Oligotrophic lakes generally host very little or no aquatic vegetation and are relatively clear, while eutrophic lakes tend to host large quantities of organisms, including algal blooms. Each trophic class supports different types of fish and other organisms, as well. If the algal biomass in a lake reaches too high a concentration, massive fish die-offs may occur as decomposing biomass deoxygenates the water.

Yankee Lake is classified as a Mesotrophic lake – meaning it has moderate productivity. CSLAP monitoring shows that the lake’s water quality is generally stable and healthy. Key indicators like water clarity, algae (chlorophyll‐a), and nutrients (phosphorus) all reflect moderate (mesotrophic) levels, consistent with a lake that is neither nutrient-poor nor excessively nutrient-rich. The lake’s pH hovers around neutral (~7), with soft water (low hardness) and low color (not too much chlorophyll), indicating clear, low-tannin water. Overall, Yankee Lake’s conditions support recreation and aquatic life, with no chronic water quality impairments noted.

Trend Summary

Long-term data indicate no major degradation in core water quality measures over the past two decades. However, some gradual changes have been observed, notably, specific conductance (a measure of dissolved salts) has increased significantly since 2006, and surface water temperatures have risen slightly in the same period. These trends suggest increasing road salt runoff and the influence of climate warming as areas to watch. Importantly, no aquatic invasive species have been found in the lake to date, and harmful algal blooms (HABs) have been rare and low in toxicity when they did occur. The sections below analyze each water quality indicator in detail, using a color-coded status (🟢 Green = Good, 🟡 Yellow = Caution, 🔴 Red = Concern) to highlight areas of concern for lake health and safety.

Water Quality Indicators and Trends

Nutrient Levels (Total Phosphorus and Nitrogen) – 🟢 Green (Good)

Total Phosphorus (TP): Phosphorus levels in Yankee Lake remain low to moderate, characteristic of mesotrophic conditions. Summer surface total phosphorus generally ranges around 0.005–0.020 mg/L, with 2019 values near the lower end of that range. These concentrations are well below eutrophic levels and indicate that the lake is not overly enriched with nutrients. In fact, the 2019 seasonal average total phosphorus fell in the oligotrophic to low-mesotrophic range, which is a positive sign for controlling algae growth. There is no evidence of a rising phosphorus trend; if anything, total phosphorus has been fairly stable or slightly declining compared to a decade ago (a spike observed in the late 2000s had subsided by 2018–19). Current phosphorus levels are supportive of good water quality, and keeping total phosphorus low will continue to be crucial for preventing algal blooms.

Total Nitrogen (TN): Total nitrogen in the lake is moderate, typically about 0.3–0.5 mg/L in summer. Most of the nitrogen is in soluble forms (nitrate, ammonia), which means it is readily available for uptake by algae. The lake’s nitrogen-to-phosphorus (N:P) ratios are often quite high (well above 15:1 on average), indicating the lake is usually phosphorus-limited. In other words, phosphorus is the nutrient in shortest supply relative to algae’s needs, which helps keep excessive algal growth in check. Overall, nutrient levels earn a Green rating: both total phosphorus and total nitrogen are within ranges expected for a healthy, moderately productive lake, and there have been no significant increases in nutrient concentrations in recent years. Continued vigilance is needed to ensure septic systems and runoff do not elevate phosphorus going forward, but current conditions are good.

Algal Growth (Chlorophyll‐a and Algal Blooms) – 🟢 Green (Good)

Chlorophyll-a: Measurements of chlorophyll-a, which indicate the amount of algae in the water, show moderate algal abundance consistent with mesotrophic status. Summer chlorophyll-a averages have typically been in the 3–6 µg/L range, sometimes peaking slightly higher late in the season but generally staying well below levels associated with algal nuisances. For example, 2019 chlorophyll-a averaged ~3.3 µg/L, reflecting moderate algae levels. These values are far from eutrophic (high algal) conditions and contribute to the decent water clarity. The lake’s open-water algal community is usually dominated by benign green algae and diatoms, with low levels of cyanobacteria (blue-green algae) present. This balance is favorable, as green algae and diatoms are less likely to produce toxins. There is no sign of worsening algal blooms in the monitored period – chlorophyll concentrations have remained relatively stable year to year. Thus, algal levels are rated Green, indicating a healthy, balanced plankton community at present.

Harmful Algal Blooms (HABs): Caution is warranted regarding Harmful Algal Blooms, even though they have been documented only once. Water quality conditions generally indicate low susceptibility to severe blooms, and no open-water Harmful Algal Blooms have been reported. The open-water toxin levels have consistently remained below recreational health thresholds. However, one isolated shoreline bloom has occurred: A small localized bloom was documented in July 2019, comprised mainly of cyanobacteria (identified as Aphanocapsa, a blue-green alga). In that event, the blue-green chlorophyll level far exceeded the Harmful Algal Bloom threshold (one sample had extremely high cell density), but fortunately laboratory tests found no detectable microcystin toxin in the sample. In subsequent years, the lake did not experience any Harmful Algal Bloom outbreaks, according to CSLAP records and the New York State Department of Environmental Conservation’s Harmful Algal Bloom notification archives. Yankee Lake did not appear on the New York State Department of Environmental Conservation’s 2023 or 2024 Harmful Algal Bloom advisory list. This suggests that, while the lake can occasionally develop a bloom under the right conditions (e.g. hot, calm weather after nutrient pulses), it’s not prone to chronic or frequent Harmful Algal Blooms. We assign a Yellow (Caution) for Harmful Algal Blooms: The overall risk is moderate to low, but because even a rare toxic bloom could pose a serious health risk to people and pets, vigilance is needed. The community should continue to monitor for Harmful Algal Blooms and treat any suspected bloom as potentially toxic until proven otherwise. (As a reminder: Harmful Algal Blooms in fresh water often look like spilled paint or pea soup; if observed, avoid contact and report it immediately.)

Water Clarity (Secchi Disk Transparency) – 🟢 Green (Good)

Water clarity in Yankee Lake is moderate to good and typical of a mesotrophic lake. Secchi disk transparency readings during summer generally range from about 2.5 to 3.5 meters. In 2019 the average clarity was ~2.9 m​eters, and in 2022–2023 Secchi readings continued to fall in the 2.5–3 meter range, with clarity usually a bit higher in early summer and slightly lower in late summer as algae and sediments increase. These Secchi depths correspond to moderate water clarity – one can typically see the lake bottom in shallower areas, and several feet deep in open areas. The clarity is far from the murky conditions of eutrophic lakes, though not as crystal-clear as an oligotrophic lake. There has been no significant long-term decline in clarity; if anything, clarity has been quite consistent over the years, with fluctuations mostly driven by seasonal algae growth and runoff after a rain.

Overall, Yankee Lake’s transparency is sufficient to support recreation (swimming, boating) and aesthetic enjoyment. We rate water clarity as Green (Good). It’s worth noting that being a shallow lake, heavy rains or boat activity can stir up bottom sediments and temporarily reduce clarity, and late-summer algae can tint the water greenish – but these effects have been minor. The lake’s clarity is in line with expectations and even better than many nearby lakes of similar productivity.

pH and Water Chemistry – 🟢 Green (Good)

The lake’s pH is generally in the 6.5 to 7.5 range, indicating neutral conditions which are ideal for most aquatic life. In most recent sampling, surface pH averaged about 7.0–7.3​. Occasional readings have hit slightly acidic (~6.3) or slightly alkaline (~7.8) values, likely due to natural fluctuations (e.g. rainfall events or algal activity), but the pH stays well within New York State water quality standards and is considered normal. The neutral pH means the lake is not overly acidic (acid rain is not a major issue here), and has some buffering capacity despite soft water.

Water hardness and alkalinity are low. Calcium levels were around 2–6 mg/L in recent years, reflecting very soft water with low mineral content. This low calcium translates to low hardness and alkalinity. While low hardness means the water has little buffering against pH change, the lake’s pH has remained stable, likely thanks to the surrounding geology and minimal acid inputs.

One benefit of low calcium is that Yankee Lake is not susceptible to zebra mussels – zebra mussels generally require >20 mg/L Ca to thrive, so the lake’s chemistry provides a natural defense against that particular invasive species. Conductivity (discussed below) has been rising, but overall the ionic balance of the lake is still favorable (no extreme salinity or pollution indicated yet). In summary, pH and basic chemistry earn a Green rating, as they are within healthy ranges. Continued monitoring is wise to detect any future shifts (for instance, if alkalinity were to drop or salt inputs increase further).

Temperature and Oxygen Profiles – 🟡 Yellow (Monitor)

Temperature: As a shallow lake, Yankee Lake warms up considerably in summer and tends to mix top-to-bottom. Surface water temperatures in mid-summer typically reach the mid-to-upper 20s °C (≈ 75–85 °F). For example, in 2019 the surface temperature climbed to ~29°C (84°F) during July, and similar highs have been recorded in recent hot summers. Such warm temperatures are common for a lake of this depth, but they do mean that cold-water fish species (like trout) cannot survive here in summer – the lake’s fishery is instead suited to warm-water species. Near the bottom (~3–4 meters depth), temperatures tend to be only slightly cooler than the surface (often only a 1–3°C difference), indicating weak stratification. Essentially, the lake mixes enough that it doesn’t maintain a cold deep layer in summer; the entire water column becomes warm.

Long-term, there is evidence of a warming trend: CSLAP analyses detected a slight but steady increase in summer surface water temps since 2006. This mirrors regional climate patterns. We mark temperature as Yellow because continued warming could have ecological effects (for instance, it can extend the growing season for algae and favor cyanobacteria). At present, the temperatures are not causing any known water-quality violations, but they do warrant attention as a climate-related stressor.

Dissolved Oxygen: Routine CSLAP reports for Yankee Lake focus on surface water quality; however, given the lake’s shallow depth, oxygen depletion in deep water is possible at night or late in the summer. There is no indication of severe anoxia (complete oxygen loss) in the data – no fish kills or chemical signs of anoxia (like high deep-water phosphorus) have been noted. During the day, photosynthesis by algae and mixing likely keeps oxygen adequate throughout most of the water column. If the lake stratifies on hot calm days, the bottom layer could experience some oxygen drop, but likely not enough to cause major issues given the lake’s shallowness and periodic mixing. Overall, oxygen levels are presumed sufficient for the warm-water biota present, but it’s something to monitor, especially if nutrient levels or temperatures rise. The Yellow rating here is mainly for temperature (and its future implications); oxygen is currently acceptable, though the community should be aware that very warm water holds less oxygen, which could stress fish during heat waves.

Conductivity and Chloride (Salt Levels) – 🟡 Yellow (Caution)

One area of concern in Yankee Lake’s water chemistry is the increasing conductivity and chloride levels, which point to rising salt and mineral content in the water. Specific conductance in 2019 averaged around 150–200 µS/cm (microsiemens per cm). This is still within a normal range for New York lakes, but notably it represents a significant increase compared to a decade prior. In fact, long-term data since 2006 show that conductivity has roughly doubled since the mid-2000s, a statistically significant upward trend. The likely culprit is road runoff (winter de-icing salt) entering the lake watershed. Measured chloride ion concentrations were about 40–45 mg/L in recent samples, which, while not extreme, are elevated above natural background levels. The key point is that chloride accumulates over time. What flows into the lake, stays in the lake. Elevated chloride from road salt can harm freshwater ecosystems (it can stress or exclude sensitive organisms). Yankee Lake’s chloride is not yet at harmful levels for most aquatic life, but the upward trend is concerning – if it continues, the lake could inch toward thresholds of concern over time.

We assign a Yellow status here to highlight the need for preventative action. The lake is currently “mesohaline” (moderately salty) but not in violation of any standard. However, each spring’s snowmelt likely delivers pulses of salt that gradually accumulate. Aside from ecological impacts, higher salt content can also affect the lake’s stratification and contribute to greater water density differences. The community should keep an eye on conductivity / chloride in future monitoring. Engaging local highway departments about salt use or implementing runoff controls may be necessary if this trend continues. In short, conductivity is a yellow-flag indicator – fine for now, but trending in the wrong direction and worth addressing proactively.

Aquatic Invasive Species (AIS) – 🟢 Green (Good)

Current status: Encouragingly, no invasive aquatic plants or animals have been reported in Yankee Lake through 2024. Surveys and volunteer observations have not found problem species like Eurasian watermilfoil, water chestnut, or zebra mussels in the lake. The prior reports of phragmites (an invasive tall reed) have not shown escalation over the decade. This is a critical element of the lake’s health, as invasives can rapidly alter habitat and water quality. The lake’s water chemistry (very low calcium) provides a natural protection against zebra mussels and other shelled invaders. Additionally, being a private lake with controlled access greatly reduces the risk of introduction from boat traffic.

Vulnerability: While current conditions are good, Aquatic Invasive Species remain a looming threat. CSLAP assessments note “invasives nearby, low vulnerability” for Yankee Lake. This means some invasive species are present in the region (nearby waterbodies), but Yankee Lake’s conditions make it somewhat less likely for them to establish. Low calcium deters zebra mussels; however, invasive plants like milfoil, phragmites, or curly-leaf pondweed could potentially grow since they aren’t limited by calcium. We maintain a Green rating for now because the lake is invasive-free, but underscore the importance of continued vigilance (see Recommendations). The lake community’s efforts in inspecting visiting boats and educating residents have been effective so far – those efforts must continue to keep this indicator green.

Recreational Suitability – 🟢 Green (Good)

Volunteer assessments and user feedback indicate that Yankee Lake offers generally good recreational conditions. Swimmers, anglers, and boaters usually find the water “favorable” for recreation, with only minor, occasional impairments. Water clarity is sufficient for swimming, and algal greenness is seldom at a level that would discourage use. Aquatic plant growth is present (as expected in a shallow lake) but not described as “dense weeds” or a serious nuisance in recent reports. In fact, compared to other nearby lakes, Yankee Lake “usually has more favorable recreational assessments” – meaning people rate its swimability and overall water quality higher than peer lakes in the area.

On the 1 (best) to 5 (worst) CSLAP perception scales, Yankee Lake is typically rated in the 1–2 range for enjoyment (e.g. “beautiful” or “slightly impaired” at worst). There have been instances late in the summer where surface weeds or algae make the lake “slightly impaired” for activities, but these are limited in scope and duration. No closures or advisories occurred in the period 2019–2024. Overall, the lake’s aesthetics and usability remain good, earning a Green designation. To maintain this, the community should remain attentive to early signs of any issues (like algal scums or invasive weeds) so that recreation can continue unhindered. As of 2024, residents and visitors can generally boat, fish, and swim in Yankee Lake with confidence in the water’s quality and safety.

Summary of Lake Health

In summary, Yankee Lake’s health is predominantly good, with most water quality indicators in the Green range. The lake continues to be mesotrophic (moderately productive), balancing clarity and nutrient levels in a way that supports aquatic life without frequent blooms or oxygen problems. Total phosphorus and chlorophyll-a remain moderate, and clarity is stable – crucial factors that help prevent nuisance algal blooms. The lake’s pH is neutral and stable, and no acidification issues are present. No invasive species have invaded the ecosystem, preserving the natural aquatic plant community and habitat structure. Harmful algal blooms have been rare and low-toxicity; nevertheless, they represent an area to watch closely given the potential risk to humans and pets. The main emerging concern is the incremental increase in salt (conductivity), likely from road runoff, which is something the community can address before it becomes a serious problem. Surface water temperatures are inching upward with climate trends, which could influence the lake’s future algal and ecological dynamics.

Crucially, no Red (high concern) conditions were identified in recent reports – an excellent sign. Yankee Lake’s overall trophic state and water quality have not deteriorated in the 2019–2024 period; if anything, the lake has shown resilience and steady conditions through varying weather years. The continued engagement in CSLAP by the Yankee Lake Preservation Association (YLPA) – with sampling resumed in 2022 after a Covid-driven hiatus – has provided valuable data to confirm these trends. To ensure the lake stays healthy and safe, proactive management is needed for the cautionary Yellow areas (HAB potential, salt, climate adaptation). A separate section provided recommendations to the YLPA Board of Directors to address the Yellow areas of concern, and gave suggestions for maintaining the Green indicators for years to come.

Sources

The 1,730 Yankee Lake data points collected from 2005 through 2024 under the auspicies of the New York Citizens Statewide Lake Assessment Program (CSLAP) were analyzed for determining trends, patterns, and issues, with special emphasis on the last five years. The Yankee Lake web site provided additional contextual definition of Yankee Lake and its community, and an understanding of the roles and responsibilities of the Yankee Lake Preservation Association. Key information on the lake’s trophic state, water quality trends, and stewardship recommendations are derived from NYSDEC, NYSFOLA and CSLAP references, and these CSLAP Yankee Lake summary reports:

• 2019 CSLAP Report Yankee Lake
• 2022 CSLAP Report Yankee Lake
• 2023 CSLAP Report Yankee Lake
• 2024 CSLAP Report Yankee Lake

These reports provide detailed measurements and context for Yankee Lake’s condition and form the basis for our color-coded health assessment. Additional guidance on HABs and lake protection measures is taken from NYSDEC and YLPA materials.

• Harmful Algal Blooms | Yankee Lake Preservation Association
• 2024 CSLAP Report Yankee Lake

By integrating these data and guidelines, this report provides a comprehensive overview of Yankee Lake’s water quality and a roadmap for its continued preservation.