Thank goodness for the Department of Natural resources in Minnesota who was on hand to raise fish in captivity and release them after some thoughtless beaver dams raised the water temperatures and made it impossible for trout to live. Thank goodness they’re always on hand to issue permits to kill those beavers. Thank goodness they were able to sprinkle fish food and the spotted browns wouldn’t be dependent on the toxic, barely life-suporting streams to sustain them. Thank goodness we killed all the bears that would have eaten them and have plenty of fishermen on the bank to remove them after a short stay in the dead stream. Thank goodness we can drive in our cars to fish by the waters edge for a few hours and enjoy unnatural nature.
DNR Fisheries Specialist Jim Levitt said the agency releases brown trout in Brown’s Creek every spring to boost the creek’s fish population… Another natural impact on Brown’s Creek trout is the beaver, according to Levitt. Beaver dams on the creek slows the flow and warms up the creek’s water.
There are beaver myths that I can argue again and again without losing my temper. There are misunderstandings where I can genuinely see that the right information will make things clearer. There are chuckle-worthy half-hearted attempts to confuse the masses that will unhappily crumble in the face of data. But the determined, malicious, and federally funded scatology arguing that beaver dams kill fish by raising pond temperatures I have NO patience for. Among other things, it is a transparent attempt to exonerate our damn pollutions by blaming the dam beaver instead!
Let’s pretend, for the moment, that the scatology was accurate. Lets say that beaver dams DID raise temperatures all through the pond, and the fish got all hot and sweaty. How much worse a problem that must have been when we had 60,000,000 or more beavers! You know, back before the fur trade when beavers were once in “every river, brook and rill” (Samuel de Champlain). They must have turned all our streams into hotubs. I bet our trout numbers must have been abysmal back then!
Except they weren’t. You know they weren’t. I know they weren’t. Every man, woman and child, scientist and historian, knows they weren’t. Fish were once crazy plentiful and sustained a population who survived on them, including the bears. There was no Department of Natural Resources, but there were plenty of natural resources to go around . How is this possible?
HYPORHEIC exchange. Say it with me now. The water you see in a stream is just part of the story. Water is underground too. That’s why we put wells in the ground. The water in the ground is much, much colder than the water in the stream because the sun’s not shining on it. That cold water seeps through the banks of the beaver pond and it mixes with the water that’s already there. Water from the stream seeps back through the bank and gets stored underground too. That’s how beaver dams raise the water table.
Check out this slide from the talk we did with Michael Pollock in Yosemite. The headwaters of the stream are cooler, and the water gets warmer as it flows down hill because its been in the sun longer. The big exception to this is the site of the beaver dam, where pooled waters are getting infused by huporheic exchange. Think of the beaver pond like a way station, a rest stop along the marathon route. While the water pauses in its journey it, it is refreshed with cooler water. And since the pond retains more water than the stream that continues on, water from the pond is forced into the banks, travels underground and re-emerges down stream, on the other side of the dam.
Which means if you want cooler temperatures, and more trout, you need MORE beaver dams – not fewer.
