IDFG to explain Dworshak nutrient program
Agency has been fertilizing the reservoir since 2007 to boost fish size
Idaho Fish and Game officials will present information and answer questions Wednesday in Orofino about a program that adds nutrients to Dworshak Reservoir but has some people worried it is causing unintended consequences.
The five-year pilot program managed by the department and the U.S. Army Corps of Engineers is attempting to spur growth of phytoplankton in the 55-mile-long reservoir on the North Fork of the Clearwater River. Biologists want to know if adding a mix of nutrients to boost plankton growth can resonate up the food chain and lead to bigger kokanee, a land-locked salmon that is a popular fishing target there.
The experimental releases began in 2007, and preliminary results suggest they are producing modestly bigger fish.
Some people, however, are concerned the nutrients might also be producing negative side-effects. Some swimmers have reported mild rashes after swimming in the reservoir, and there is concern the program might be leading to algae blooms that could be contributing to steelhead disease problems at Dworshak National Fish Hatchery downstream of Dworshak Dam.
Earlier this month, an Orofino man filed a notice of intent to sue the two agencies, alleging officials did not secure the necessary permits to release nutrients in the reservoir.
“There has just been a lot of letters to the editor about negative effects and we have received a ton of phone calls from people asking questions. We decided let’s have a public meeting and inform the public what we know and try to stop some of the rumors and at least get people real data,” said Joe DuPont, regional fish manager for the department at Lewiston.
DuPont said he can’t say the program isn’t the cause of rashes or the problems at the hatchery.
“We have data and can only tell what the data says.”
He did say that swimming rashes in general can be caused by the growth of blue-green algae. There was a bloom of the algae in the reservoir two years ago.
“It was worse in the unfertilized arms (of the reservoir). They have been doing fertilization in a lot of different water bodies and have found you can actually reduce blue-green algae supply if you do it properly.”
In the past two years, steelhead production at Dworshak Hatchery has been hampered by outbreaks of a disease known as IHN. Biologists say the disease is found in the North Fork of the Clearwater River, from where the hatchery draws its water. But some have suggested algae growing in the reservoir and released through the dam might be irritating the gills of juvenile steelhead at the hatchery and making them more susceptible to the disease.
DuPont said the department is in the process of studying the link among algae, fertilization and the steelhead disease outbreak.
The program is in its fourth year. This year, DuPont said kokanee in the reservoir appear to be fatter but not longer. He said extra girth put on by the fish can help them survive winters.
“In 2006 we had a huge number of kokanee and their body condition was fairly poor and there was a big die-off over the winter. A fatter fish should be able to withstand winter pressure more than a thinner fish.”
After the final year of the project, Fish and Game and corps officials will review their data and determine if the program should continue.
Fisheries biologist Sean Wilson and other Fish and Game officials will hold the meeting from 7 to 9 p.m. in the gymnasium at Orofino High School.