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Tropical Storm Irene
What Happened to Fish and their Habitat after the Flood


jumping trout

Tropical Storm Irene pummeled Vermont on August 28, 2011, causing dramatic flooding and widespread damage to roads, bridges, buildings, homes and property in over half the state. Not since the great flood of 1927 had Vermont seen such widespread and extreme flooding. Yet, Vermont has seen more frequent flooding on a more localized basis, including in 1973 and several other times since 2011.

A year after Irene, what happened to so many Vermonters in so many towns is well known. But what happened to our fish as the rivers churned? Unlike the readily visible changes that occurred in many rivers, what happened in the living underwater world cannot be readily seen. Let’s take a look... with a focus on our treasured trout populations.

Trout need good habitat -- what does good habitat look like?

Good habitat has a mix of large boulders, fallen trees, cobbles, gravels and forested shoreline. There is a mix of fast and slow currents, of deep and shallow areas.

Healthy habitat = healthy fish populations

good trout habitat

Poor habitat looks a lot different. This stream has been straightened and widened with the large rocks and trees removed, resulting in a featureless stream channel with poor aquatic habitat value.

bad trout habitat

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What happened to the trout after Irene?
Department surveys in the Mad and Dog River watersheds showed that trout numbers declined to 33-58% of pre-flood levels.

trout populations graph

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Will fish populations recover?
Fish have survived floods and droughts for thousands of years, and are well adapted to survive and recover relatively quickly. A devastating flood reduced trout numbers in Clay Brook in 1998 but they rebounded within a few years. While significant changes to the physical habitat occurred following the flood, the overall quality of the habitat remained in tact.

However, where the habitat no longer exists, recovery will take many years, if not decades. Unfortunately, much damage was done to our streams by our own activities after the waters receded. The Rivers Program of the Department of Environmental Conservation, estimates that 40% of the river repairs done after Irene may actually have increased our vulnerability to damages during future floods.

Department biologists are surveying Vermont’s streams, but it’s too early to quantify the effects of the storm.

trout population comparison graph

Floods play a positive role in renewing fish habitat.
As damaging as floods can sometimes be, they also are part of a natural process by which a river renews and maintains itself over the long term. Floods recruit large trees, refresh gravel deposits, and cause localized scour, resulting in high quality habitat conditions. The fallen trees shown in the photo promote pool formation and excellent hiding places for fish.

flooding benefits

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Will we do better next time?
The floods of 2011 won’t be the last, so we need to learn from our mistakes and better prepare for the next time. Irene showed us that we can’t control rivers and that we need to learn to live in harmony, recognizing the amount of room a river needs. Preventing flood damage and protecting our rivers go had in hand. Our understanding of the science of how rivers behave has advanced a great deal in recent years, and we are well-positioned to chart a better path forward. Let’s work together at both the state and community levels to effectively reduce the potential for future flood damage in a way that respects and conserves our natural resources.

stream fishing

Fortunately, Vermont still has abundant opportunities for great wild trout fishing. While some rivers were damaged, most were not. Biologists are surveying trout populations this summer, and early reports indicate that healthy wild trout populations are still present in quite a few locations.

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