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Lake Simcoe Region Conservation Authority

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​​​​​​A stream flowing through a forest. The stream is surrounded by trees.

Stream and River Ecosystems

Warming water temperatures, reduced snowpack, more frequent drought, and more extreme precipitation patterns will alter habitats for local aquatic species. Since individual species have specific habitat requirements, some species may be able to cope with or even thrive under new conditions, while others may struggle.​

Loss of Coldwater Fish Habitat

Coldwater streams have always been managed as the most sensitive features on the landscape. Under future climate change conditions it is expected that only 12% of the watershed’s streams will remain cold by 2065. In response to warming streams with less dissolved oxygen, coldwater fish will seek refuge in these few remaining cooler groundwater-fed streams. Crowded into ever-shrinking habitat, populations of coldwater species such as brook trout may become stressed, increasing their susceptibility to disease, competition for resources and risk of predation for juveniles.

Fish Reproduction

Since both water temperature and streamflow changes are cues for fish to spawn, climate change is expected to affect spawning success. For example, an earlier spring thaw or erosion from extreme weather events is likely to reduce reproductive success and survival of young fish. Overall, a changing expected to have negative impacts that may reduce reproductive success, meaning fewer fish in the tributaries.

Other Indicator Species

Aquatic insects, worms and mollusks that live on the bottom of streams are excellent indicators of water quality. The changes in stream flow, temperature, and water quality described above may lead to changes in these communities, including a shift towards more generalist species with higher thermal tolerances, at the expense of more sensitive species and overall species diversity may decrease.​