Weather’s Influence on Water Quality
Compared to last year where Maine saw record rainfall events, this summer has been hotter and drier. Weather conditions are a major influence on lake water quality, with lakes responding differently based on interacting characteristics like lake depth, water chemistry, and erosion.
Heavier rainfall means increased runoff and erosion around the watershed, which introduces sediment to the lakes that contains phosphorus — a key nutrient required for the growth of algae. Not only does more rain lead to reduced water clarity because of debris and floating particles, but also because of the potential for excess algae growth due to greater phosphorus availability. Current water clarity is better compared to July 2023 on Long Pond (Upper and Lower), Great Pond, Salmon Lake, McGrath Pond and Messalonskee Lake (see table below).
| East | -7 ft | McGrath | +5 ft |
| Great | +1 ft | Messalonskee | +1 ft |
| Long (Lower) | +3 ft | North | -9 ft |
| Long (Upper) | +2 ft | Salmon | +5 ft |
Meanwhile, the two shallower water bodies, East Pond and North Pond both have poor water clarity this year due to an increase in cyanobacteria growth. Cyanobacteria are a type of microorganism that can thrive in warm waters due to excess nutrients like phosphorus. The hot temperatures at the end of June last month initiated a severe algae bloom in North Pond (defined as water clarity lower than 2 meters/6.5 feet by the Maine Department of Environmental Protection). While East Pond’s water clarity is poorer than last year, it is 6 feet better than it was in July 2017, before the 2018 alum treatment. We do not expect East Pond to reach severe bloom status like North Pond.
While last year’s cooler weather coincided with better water quality for North Pond and East Pond, this year’s drier weather coincides with better clarity among the deeper lakes. However, every rainfall results in runoff, and reducing erosion on your property is the best way to ensure that minimal amounts of nutrients will enter the lake when it rains. A changing, unpredictable climate is not something we can control, but we can collectively do a great deal to minimize the impacts of erosion on every property in the Belgrade Lakes watershed.
Note that cyanobacteria are ubiquitous; in addition to being among the oldest organisms on Earth and the first to produce oxygen, cyanobacteria are the most widely dispersed algae on the planet and can be found in nearly every terrestrial, freshwater, and marine environment. The cyanobacteria Dolichospermum that is currently blooming in North Pond has also been found in every other lake in the Belgrades this season. The reason Dolichospermum has grown excessively in North Pond is due to excess phosphorus that is released from the lake sediment when deep-water oxygen is depleted throughout the summer.
While some types of cyanobacteria can produce harmful toxins, we have not detected any toxins in our routine monitoring. However, we advise that you do not swim in algal scums, and to not swim in water bodies if you cannot see your feet in the water. We partner with Colby College to collect and analyze samples for water and sediment chemistry on North Pond and all the other lakes to understand lake ecosystems and develop science-based strategies to improve water quality.
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