Spawning Gravel Projects

With the system of dams and diversions in the Boise River there is a lack of spawning gravel recruitment into the lower Boise River, and this situation has some negative implications for the fishery. Trout Unlimited took the lead to implement projects more than fifteen years ago. But first let’s look at a recent project.

First, our Heron Park spawning gravel project in 2019-2020 was the brain child of a couple chapter members who were aware of bank revegetation work in Garden City. With a coffer dam planned to dewater the bank for the construction, a permit to fill large geotextile bags with clean spawning gravel was approved by the US Army Corps of Engineers and Idaho Department of Water Resources.

The white bags are “super sacks” full of clean suitable sized spawning gravels.

Typically a cofferdam will use road mix or other fill material and the bags will be lifted into place and then lifted out when the work is done. In this case the bags were cut and the fabric removed and the gravel left in the Boise River.

March 14, 2020 photo shows the bank a year later and the gravels in the river. And a trout spawning redd where the bottom of the stream is lighter in color.

In early 2020 as the pandemic was setting in there was an opportunity to walk along the river bank and the first hint of spawning success was commotion at the stream edge when some rather large trout bolted for deeper water. The second indicator was a redd in the spawning gravel.

A closer look at the trout spawning redd, March 14, 2020.

Second, we go back in time to our Heron Creek Project in east Boise (not to be confused with Heron Park in Garden City several miles west), and a tumblr entry in 2011 showing a redd where spawning gravels were placed in September 2009.

And here’s a video of the spawning gravel placement in 2009 where we used a bucket brigade of volunteers:

Back in 2005 we placed spawning gravel in two side channels of the Boise River. One at Warm Springs Golf Course behind the number 10 green. The other is on the south side of the river across from the golf course at the Island Side Channel. Here are some photos:

Adding gravel to the channel behind the number 10 green at Warm Springs Golf Course.
Dick Frencer with Boise Valley Fly Fishers carries a bucket of spawning gravel, filled by the guy with the shovel who happens to be Boise Mayor David Bieter, July 16, 2005
On the Island Side Channel the gravel was placed by hand and buckets passed around.