Piling rocks across a small stream on a hot day to create a private forest wading pool may seem harmless to hikers and campers, but fish have a different point of view.
Recreational dams can block a fish’s daily needs for migrating or moving to feeding areas and cooler water.
“These last few years, with air temperatures higher earlier, the ‘normal’ rock dams load has exploded in Washington,” said Teresa Scott, Washington Department of Fish and Wildlife drought coordinator.
Building dams out of rocks and logs across a creek to form a swimming hole violates state hydraulics regulations. Left in place, even a small dam can inhibit young fish movements and migrations and can cause flooding during storms or even months later during runoff.
The majority of people we contact are just having fun and don’t realize they’re blocking fish runs.
Perry Harvester, Washington Department of Fish and Wildlife’s regional habitat program manager in Yakima
In some cases, spawning chinook salmon have been completely blocked in certain tributaries, said Perry Harvester, the agency’s regional habitat program manager in Yakima.
“Because there’s such a problem in the upper Yakima Basin, we have a small regional crew funded mostly by commercial fishing dollars, and all they do most of the summer is educate the public and remove dams by the dozens,” he said. “The majority of people we contact are just having fun and don’t realize they’re blocking fish runs.”
Most of the dams are on streams near campgrounds. “It’s an annual problem,” he said.
In some cases, the dams are built by poachers to ambush adult salmon, steelhead or bull trout heading upstream to spawn, he said.
“People have been making recreational dams forever, but for whatever reason, they have become much more of a problem in the last six years or so,” said Harvester, who’s surveyed virtually all of Washington’s salmon-steelhead streams in the Columbia Basin during his 30-year career.
A Spokane Mountaineers volunteer trail maintenance crew had a some unexpected work to do on a recent Idaho mission to Marie Creek Trail, which is north of the Wolf Lodge area at the northeast end of Lake Coeur d’Alene.
The volunteers usually deal with natural forces such as clearing new brush growth, sawing out downfall and restoring paths through landslides, said club trail work coordinator Lynn Smith. Human-made dam projects add another chore to the list.
Dams made by the public for fun have joined stream-bank destruction, poaching and other factors in the suite of threats to endangered fisheries such as bull trout, salmon and steelhead.
“It was a bank-to-bank construction that looked way more involved than just kids rearranging some stream rocks on a family hike,” Smith said. “At this time of year, the water is lower and warmer with less oxygen, so the fish we saw in the wide shallow pool needed to be able to move around to find optimum conditions.”
The volunteers waded in to scatter the rocks and restore the natural course of the creek.
“We did place some stepping stones, but left the stream free-flowing, not strained through the rock dam,” Smith said.
Scott said Washington fisheries staffers “and partners such as the Mid-Columbia Fisheries Enhancement Group monitor for rock dams in the upper reaches of east side streams, but there’s never enough staff capacity to get to all the likely locations.”
“With stream flows lower on the west side in 2015 and earlier this year, we have seen a lot more rock dams in Western Washington lately,” she said.
“WDFW started to see rock dams in south Puget Sound creeks as soon as the air and water temperatures began to soar in 2015 — as early as May.”
Spring chinook start spawning as early as the end of July up the Naches River tributaries and bull trout start spawning in August, when they are especially impacted by recreation dams in low flows.
Dams made by the public for fun have joined stream-bank destruction, poaching and other factors in the suite of threats to endangered fisheries such as bull trout, salmon and steelhead, Harvester said.
Dams artificially concentrate the fish, exposing them — especially big migrating fish — to stress, predators and poachers.
“This is such a difficult issue, because WDFW wants people to feel connected to their local natural areas,” Scott said. “But fish need to be able to move up and down stream to find cool water and eventually to spawn.”
Rock dams vs. beaver dams
Beaver dams generally are beneficial to fisheries as opposed to illegal recreational dams, which have no redeeming values for fish, a fisheries biologist says.
“Beaver dams usually are built higher in the watersheds and on lower gradient areas,” said Perry Harvester, Washington Department of Fish and Wildlife regional habitat manager in Yakima.
Coho and steelhead have an advantage in some areas with beaver dams because some of the fish can negotiate the dams and the fry prosper in the better cover and abundant food sources, he said.
Beaver dams can be natural hatcheries, he said.
“Our crews sometimes help the fish by cutting little notches in the beaver dams at the appropriate times. All it takes then is one good rain or runoff event to stimulate fish movements.”
“The salmon and steelhead that migrate downstream out of beaver dams are some of the most fit and healthy fish we see. They’re fat, sassy little buggers that have a high rate of survival as they emigrate to the ocean.”