8984-R2_NewGloucester_2023-2024_AnnualReport_Web

2024 Sabbathday Lake Water Quality Report Table 3. Average Annual Chl-a monitoring for Sabbathday Lake, Station 1 (1975-2024). Chl-a readings in Sabbathday Lake have ranged from 1.6 ppb (1998, 1999, 2000) to 12 ppb (2023). In 2024, Chl-a remained decreased over the course of the summer from 2.9 ppb in July, to 2.5 ppb in August, and 2 ppb in September. Average annual Chl-a was 2.5 in 2024, less than both the historical and 10 year averages. Statewide, Chl-a ranges from 0.1 - 208 ppb with an average of 5.7 ppb. The 10-year average for Sabbathday Lake is below the state average, 3.5 ppb compared to 5.7 ppb (Table 3). With the exception of 2023, concentrations of Chl-a in Sabbathday Lake are lower than the statewide average and have remained relatively stable over the sampling period (Table 3 & Figure 4). Chlorophyll a (ppb) Years Annual Chl-a Mean Min Max 2024 Sabbathday Lake 2.5 2.0 2.9 Historical Average (1975-2024) 3.8 2.0 8.7 10-Year Average (2015-2024) 3.5 2.0 8.7 Avg. Maine Lakes 5.7 0.1 208

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Figure 4. Average annual water quality data for trophic state indicators (water clarity, total phosphorus (TP), and Chlorophyll-a (Chl-a)) for Sabbathday Lake, Station 1.

DISSOLVED OXYGEN & TEMPERATURE Sabbathday Lake’s cold, deep water provides habitat for coldwater fish including brown trout and brook trout, along with warmwater fish such as largemouth bass, smallmouth bass, white sucker, chain pickerel, and black crappie. Coldwater fish begin to experience physiological stress at around 5 parts per million (ppm) of dissolved oxygen (DO), although tolerance for low oxygen conditions is species specific. If DO drops below 2 ppm, it can impact fish survival and even cause fish kills if there is no oxygenated habitat nearby for fish to move to. Coldwater fish generally prefer water that is less than

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