Water Quality

Total Phosphorus (TP): Phosphorus levels in Yankee Lake remain low to moderate, characteristic of mesotrophic conditions. Summer surface TP 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 TP 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, TP 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 TP low will continue to be crucial for preventing algal blooms.

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 TP and TN 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.

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. 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.

Harmful Algal Blooms (HABs): Caution is warranted regarding HABs, even though they have been documented only once. A small localized shoreline bloom was documented in July 2019, comprised mainly of cyanobacteria (identified as Aphanocapsa). Laboratory tests found no detectable microcystin toxin in the sample. In subsequent years (2020–2024), the lake did not experience any HAB outbreaks. Yankee Lake did not appear on NYSDEC's 2023 or 2024 HAB advisory list. For more details, see Harmful Algal Blooms.

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 meters, 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. There has been no significant long-term decline in clarity; if anything, clarity has been quite consistent over the years.

The lake's pH is generally in the 6.5 to 7.5 range, indicating circumneutral conditions ideal for most aquatic life. Water hardness and alkalinity are low; calcium levels were around 2–6 mg/L in recent years, reflecting very soft water. One benefit of low calcium is that Yankee Lake is not susceptible to zebra mussels – they generally require >20 mg/L Ca to thrive, so the lake's chemistry provides a natural defense against that invasive species.

Temperature: As a shallow lake, Yankee Lake warms considerably in summer and tends to mix top-to-bottom. Surface temperatures in mid-summer typically reach the mid-to-upper 20s °C (≈ 75–85 °F). Long-term, there is evidence of a warming trend: CSLAP analyses detected a slight but steady increase in summer surface water temps since 2006.

Dissolved Oxygen: No indication of severe anoxia has been observed. 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.

One area of concern is the increasing conductivity and chloride levels, which point to rising salt content. Specific conductance in 2019 averaged around 150–200 µS/cm. Long-term data 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 – elevated above natural background levels.

Encouragingly, no invasive aquatic plants or animals have been reported in Yankee Lake through 2024. The lake's water chemistry (very low calcium) provides a natural protection against zebra mussels and other shelled invaders. Being a private lake with controlled access greatly reduces the risk of introduction from boat traffic. CSLAP assessments note "invasives nearby, low vulnerability" for Yankee Lake.

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. On the 1 (best) to 5 (worst) CSLAP perception scales, Yankee Lake is typically rated in the 1–2 range for enjoyment. No closures or advisories occurred in the period 2019–2024.