Beneath the Surface of Rivers and Streams

Person holding fish in clear container filled with water.

Summer is an Important Season for Aquatic Life

During summer, water levels in streams are at their lowest and water temperatures are at their warmest. Summer is also when food is most abundant, providing wildlife the opportunity to feast heavily before the leaner, colder months return.

Aquatic Species

Late spring and early summer is when many fishes, crayfishes and aquatic insects lay eggs. As water temperatures begin to rise, minnow species like creek chub build gravel nests to lay their eggs in. Stray eggs provide a timely source of energy for other fish.

Tiny new crayfish hatchlings, which were attached to their mother’s tail, will start roaming and feeding by themselves. As spring gives way to summer, many aquatic insects like mayflies emerge and fly above the surface. As these insects complete their life cycles, they also provide surges of food for fish and other wildlife like birds and bats.

A fish in a clear container filled with water.
Creek chub

Food Abundance

Just like plants in your garden, summer is the growing season for life in our steams. Food availability increases as temperatures rise. Warm weather helps leaf litter break down faster. This provides abundant food for newly hatched fish and aquatic insects, now able to grow faster along the stream bottom. Longer and warmer days also provide aquatic species with more foraging time.

A Stressful Time

Summer can also be a stressful period for temperature sensitive aquatic species because water levels in some streams become very low or even dry up. This can result in some streams only being able to support aquatic life for part of the season. Some fish species, like brook stickleback, have adapted to low oxygen conditions and can survive in these extreme low water conditions. These fish use these habitats which are unavailable to other species. They can even be found in isolated pools.

A small fish floating in a clear holding tank.
Brook stickleback

Moving Time

As summer progresses and temperatures increase, some area streams can become too warm for coldwater dependent species such as trout. These fish will seek out colder areas with groundwater springs or small shaded tributaries. By now, fish are also less active during the middle of the day when temperatures are at their peak.

By the late summer, most of the large swarms of aquatic insects have already emerged and laid eggs. Food from streamside vegetation such as ants and grasshoppers are a late summer food source for fish. As summer fades, the push continues to feed and grow before temperatures drop and food becomes less abundant.

A stream with plants growing along the banks.
Summer is the season with the lowest water levels of the year. Photo credit: CVC’s Chelsea McIsaac

Through our Integrated Watershed Monitoring Program (IWMP), our team monitors conditions and trends in fish and aquatic insect communities in streams across the Credit River Watershed. Learn more about IWMP.

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By Phil Bird, Specialist, Watershed Monitoring

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