The Stream Doctor

March 22nd, 2004

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

Q. From Dcush23315: In the Northwest where I live and fish we have, for the past two years, been dumped on with rain and floods. Rivers have been blown out for weeks if not months. My question is how can any aquatic insect survive such forces and will we see a major decline in hatches? If you are wildly rich or have won the lotto, I may be your long lost last name is Cushing.

A. I used to live in the Northwest and am familiar with what you are talking about. However, I wouldn't be too concerned about seeing a decline in hatches for the most part. It is quite amazing to see not only how many insects actually survive severe floods, but also how fast streams can become repopulated. Much depends on how much movement of bed materials occurred. Both aspects have been widely studied throughout the world. The Touchet River in southeastern Washington suffered major flood damage. When the water receded, I visited a site where I take my Stream Ecology classes and it was literally a straight chute devoid of everything except a few chironomids; bed movement was extensive. This was in May. By June, the class was able to find an abundant variety of aquatic insects in the impacted reaches.

Repopulation comes from a variety of sources (I addressed this in relation to small cold desert spring-streams in a paper I published a few years ago). If the floods occur when egg-laying adults are present, repopulation is hastened. If it occurs in winter, repopulation may take longer depending upon the severity of the flood because egg-laying adults will have to come from nearby sources. However, many floods do not impact entire water courses but only certain reaches, leaving a rich source of recolonizers in unimpacted reaches above the flood zone which can drift down and recolonize the impacted area. It is also amazing how many aquatic insects actually survive these floods. They find refuge in the hyporheic zone (below the stream bed, again, if bed movement wasn't severe), behind larger stones not moved by the water, and some even have enough mobility to actually follow the rising water edge and then retreat with it when waters recede. The latter depends on many things; rate of water rise, nature of the stream bank, etc., but does happen in small spring-streams.

I hope this gives you some idea of the complexity of this. If you'd like to pursue it further, get in touch with me at I'm afraid you are out of luck regarding instant wealth by relationship. I'm neither rich nor do I know of any lost cousins! Great name, though.

If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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