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Climate Change Impacts:
Lakes, Streams, and Fish
Michigan's numerous rivers, streams, and lakes draw millions of anglers, boaters, birders, and beach visitors each year. Aquatic ecosystems, and species that depend on them, will be impacted by a warmer climate, land-use changes, and the introduction of invasive species.

Native aquatic plant and animal species will differ widely in their responses to changing water temperature and hydrology. Some will respond by adapting to warmer temperatures, or expanding their ranges northward, or seeking refuge in areas where temperatures and flow patterns remain suitable. Others will decline to extinction. Among the potential impacts of climate change with implications for lakes, streams, and fish in Michigan are:

• A Change in the Distribution of Fish Species
  Individual fish actively select and rapidly change living areas based on suitable temperatures, oxygen concentrations, and food availability. As water temperatures in the region increase, cold-water species such as lake trout, brook trout, and whitefish may decline dramatically, as cool-water species such as muskie and walleye, along with warm-water species, such as bluegill and smallmouth bass, expand their ranges northward. As a result of these changes, anglers may lose their preferred catch. To compensate for range and population changes, current stocking methods may need to be reevaluated.
  
  
• The Spread of Invasive Species
  A changing climate will likely favor invasive species with generalized habitat and feeding requirements over native species with more specialized needs. The spread of non-native nuisance species will likely to compound the impacts of climate change on Michigan's aquatic ecosystems. Climate change is likely to permit some invasive speices, such as zebra mussels and common carp, to expand their range northward. Their movement, along with the introduction and spread of other invasive species due to climate change, will fundamentally change native fish communities.
  
  
• Changes to Stream Flow and Habitats
  Stream ecosystems will be impacted by a the region's changing precipitation patterns of an increase in precipitation in the winter and spring and a decrease in the summer and fall. Stream responses to these changes will vary according to the relative contribution of groundwater versus surface water in their flow patterns. In general, dryer summers will lead to lower summer stream flow and less stream habitat due to drier conditions. Other potential impacts include disruption in fish and insect life cycles due to earlier ice out; increased floodplain habitat as a result of more precipitation in the winter and spring; and decreases in fish and invertebrate production as a result of more frequent heavy rainfall events.
  
  
• An Increased Summer Stratification
  Stratification of lakes occurs when a warm surface layer of water develops over cooler, deeper water. A warming climate increases the duration of summer stratification in the deep lakes. This, in turn, makes frequent and larger "dead zones"—areas of water depleted of oxygen and unable to support life—more likely to occur. Persistent dead zones can result in toxic algal blooms, foul-smelling, musty-tasting drinking water, damage to fisheries, and massive fish kills—known as "summerkill".
  
  
• Loss of Winter Ice
  Declines in the duration of winter ice on lakes are expected to continue. The loss of winter ice may be a mixed blessing for fish, reducing winterkill from oxygen deficits in shallow lakes but also jeopardizing reproduction of whitefish in the Great Lakes bays, where ice cover protects the eggs from winter storm disturbance.
  
  
• The Release of Nutrients and Contaminants
  Lower oxygen and warmer temperatures promote greater microbial decomposition and subsequent release of nutrients and contaminants from bottom sediments. Phosphorus release would be enhanced, and mercury release and uptake by biota would also likely increase—exposing humans to higher mercury levels via fish consumption.