Trout and Water Quality

by Corrina Parnapy


Many years ago, on an early Summer Adirondack fishing trip with my grandfather, I caught my first Brook Trout, and from then on was “hooked”. My obsession centered around the waters that our beloved Adirondack Brookies call home. Brook Trout, a cold-water char, can be found in many streams, ponds and lakes scattered throughout the Adirondack Park, and are sought after by many anglers.

Brook Trout require cold well oxygenated waters, that are clean, to survive. As any angler knows, the best kept trout fishing locations are off the beaten trail and surrounded by natural forests. The increase in overall water temperatures, within the Adirondacks, in combination with increased turbidity, lower oxygen levels, loss of food sources (due in part to deicing agents) loss of breeding habitat and impacts from acid rain could mean it becomes harder and harder to find native Brook Trout. 

The effect of water temperature on biological processes drives Brook Trout to select environments that allow for optimal internal functioning. Similar to how some of us can’t take the Summer’s heat, neither can Brook Trout. These temperature preferences can be so strong, that a fish will not leave cooler waters to feed on prey, that are located in warmer surface waters. These temperature preferences change as the fish grow. Waters that are suitable for juvenile fish, are generally not adequate for adults, forcing them into deeper colder waters. This can cause decreased localized food sources, overcrowding and diseases.

As the temperatures rise, there is increased evaporation and decreased water levels within lakes and streams. This can lead to increased algae growth, and then increased bacterial action, that leads to decreased oxygen levels in the colder parts of lakes, making them inhabitable to Trout and other fish species. The decreased water levels would mean that Brook Trout would lose access to portions of streams during Summer months. This, coupled with the already reduced habitat connectivity from undersized or perched culverts, could have a significant impact on our native Brook Trout. Just a couple of degrees increase in temperature impacts Brook Trout. Studies have already indicated that bodies of water, within the Adirondacks, have increased water temperatures, and are showing increased algae growth and decreased oxygen levels. This can be due to climate change, removal of near-shore riparian vegetation, dams constructed and other changes within the watershed.

Changes in water quality can be associated with what happens on the land. When rain falls and flows across areas that have impervious surfaces like roads, eroding soils and areas with no tree cover, it is called stormwater. This stormwater picks up pollutants, sediments and excessive nutrients (nitrogen and phosphorus) that then make their way unfiltered into our streams, ponds and lakes. The sediment can smother eggs, in addition to covering gills of trout, making breathing more difficult. The excessive nutrients can shift the forms of algae within a body of water, from preferred healthy forms such as diatoms, which larval fish and aquatic bugs prefer, to thick billowing clouds of chlorophyta or potentially toxic cyanobacteria. These changes to food sources, and the overall water quality, can have a negative impact on Brook Trout. Changes in water quality can cause undue stress on the fish, changing hormone levels and causing them to remain small, stunted and less vigorous.


Deicing agents, used to manage winter roads, have an impact on Brook Trout populations. Road salt application is generally measured in levels of chloride. Every body of water will differ as to what the background levels were historically, and at what level the addition of chloride will have an impact. A low nutrient (phosphorus and nitrogen) body of water, like many of those found within the Adirondacks, can experience impacts to algae (the base of the aquatic food web) at as little as between 2-10 mg/l of chloride. An increase in chloride levels will shift algae dominance from chlorophyta (green algae) to cyanobacteria (blue-green algae). Native Brook Trout populations are impacted at 250 mg/l, and there is a shift in sensitive aquatic bug populations at 220 mg/l. Many streams, within the Adirondacks, have already been identified as impacted by chloride, through water quality monitoring efforts.

Many lakes, within the Adirondacks, have been impacted by acid rain. While some bodies of water are rebounding, there can still be an impact to trout populations. Acid Rain is produced primarily from human-made emissions from burning fossil fuels. There is a limited natural addition from decaying vegetation and volcanoes. Acid Rain deposits nitrates, that can increase nitrogen loading within forests surrounding bodies of freshwater. This can lead to nitrogen saturation, and the removal of calcium and magnesium from soils, further impacting the aquatic ecosystem. The excessive nitrogen, within the forests, will make its way into streams and lakes, feeding excessive algae growth. Acid Rain will make the body of water more acidic. This shifts the species composition of algae. Acid Rain causes both phytoplankton and zooplankton populations to decrease, further removing food sources for fish species.

The major concern, with Acid Rain, is the change to pH or acidity of the water. A pH below 6.5 units will start to have an impact on Brook Trout. Below a pH of 5 units, juvenile fish species and aquatic insects are impacted and fish eggs will not hatch. Below a pH of 4.5 units, the water generally becomes unsuitable for most aquatic organisms. In surveys conducted within Adirondack lakes in the 1980’s, it was determined that over 25% had a pH below 5 units. While lakes are rebounding and Brook Trout populations found within them are coming back, there is still much concern due to other water quality impacts.

We as sportsmen and women have a role to play in protecting our natural resources, including our Adirondack Brook Trout. We need to insure that the watersheds, that feed the waters of the Adirondacks, are protected. This includes upland forests and mountain peaks. Protect along the streams and shorelines that trout rely on. Allow sensible, well-planned development, with considerations for the natural landscape, habitat connectivity, including; adequate permeable surfaces, storm water protection, upgraded septic systems, rain gardens and homes that are not overbuilt for the property and environment. Maintain adequate shoreline and riparian buffers, plant native plant species and grasses, maintain and upgrade old or non-functioning septic systems. Understand the science and get involved! Grassroots efforts and citizen involvement is very important for any protection strategy. By educating the public, municipal leaders and user groups on what is happening, changes can be made that will reduce or eliminate impacts to water quality and Brook Trout habitat. And as always, maintain our tradition of sharing our passions for hunting, fishing and recreating with future generations.

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Photo Credits:

Original drawing of Brook Trout by Corrina Parnapy

Photo of Brook Trout by Jeremy Parnapy

Photo of Little Girl with Brook Trout by Robert LeClair