Climate changes such as rising temperatures, more frequent extreme storms and changes in season precipitation rates will impact lakes, rivers and streams. As air temperatures rise, so will water temperatures in freshwater systems. Shallow waters are especially vulnerable to temperature increases, which decreases the availability of fresh water habitat for cold-water species. Warmer water temperatures in deep lakes slows down processes that add oxygen to the water, creating dead zones, or areas with less oxygen that are unable to support life. These dead zones can produce large-scale fish mortality and toxic algal blooms.
Increasing temperatures, causing earlier snowmelt, combined with higher precipitation amounts and more severe weather and flooding will impact the reproduction abilities of aquatic species. Changes in the timing of high and low stream flow creates stress on aquatic plants and animals, decreasing survival rates.
More frequent floods, which often lead to sewer system overflows can lead to disease outbreaks from water-borne bacteria.
Change in Fish Species
The changing climate impacts ecosystems and environmental systems that support freshwater habitat for fisheries. Most freshwater fish species can only survive in certain water temperature ranges or stream flow conditions. Climate change can threaten such aquatic ecosystems by altering these conditions including increasing stream temperature (which causes a corresponding decrease in oxygen levels), altering stream flow due to drought or increased storms and worsening other stressors (e.g., increased storm runoff including nutrients, pollutants and sediment) that can affect ecosystem health.
Climate change threatens to disrupt the habitat, recovery and protection of some coldwater fish species, such as trout and salmon. More broadly, cold and cool water fish may be replaced by other species better adapted to warmer water, which can allow non-native and/or invasive species to become established, as in the Great Lakes region.
The effects on fish species and aquatic life, have the potential for significantly affecting traditional subsistence fishing communities.
Warmer air and water temperatures may also expand the ranges of current invasive species, or allow new ones to establish. Invasive species can pose challenges to the success of ecosystem protection efforts ranging from large ecosystem management, such as the Great Lakes, to the restoration of coastal estuaries.