Salmon began packing into California’s rivers for their autumn journey, so a federal dam opened the taps for three weeks to keep disease from racing through the crowd before the fish could finish the run

The Bureau of Reclamation has decided to temporarily increase flows below Lewiston Dam.

This decision was made because river conditions can increase disease risk for migrating salmon.

Between August 28 and September 21, the Bureau plans to increase flows below the dam from about 450 cubic feet per second (cfs) to as much as 1,200 cfs.

Higher flows are intended to reduce disease risk during this part of the migration. The temporary increase comes as Chinook and Coho salmon begin gathering in the lower reaches of the Klamath and Trinity rivers.

Higher flows are coming to the Trinity River

These higher flows represent one of the management tools available to river operators during the migration period.

In addition, all parties involved with this plan have agreed to coordinate their efforts. These parties include representatives from the Yurok and Hoopa Valley Tribes.

The group also includes the California Department of Fish and Wildlife, the United States Fish & Wildlife Service, and the Bureau of Reclamation.

Additionally, the Bureau states that the increased flows will not impact either agricultural water supplies or municipal water supplies. It should be noted that some river users may experience a change in river conditions during this time.

Water levels are anticipated to rise, and currents will likely be stronger. The water temperatures will be colder.

Because of these factors, people who come close to or enter the river during this time are asked to exercise extreme caution.

Low flows can increase disease risk

A major reason for increasing flows is related to what happens when adult Chinook and Coho salmon migrate back from the ocean.

They typically hold in the lower reaches of the Klamath and Trinity rivers for a period of time. When adult salmon return from the ocean, they tend to stay in the lower reaches of these two rivers for a short time.

While staying in this area, there are various environmental conditions that can affect their health.

Low river levels can cause additional stress upon migrating salmon. High water temperatures can contribute to even greater stress upon migrating salmon.

The combination of low river levels and high water temperatures can increase the risk of disease spreading among adult salmon.

Stored water provides another management tool

Therefore, flows will be increased to counteract low river levels and high water temperatures. The temporary flow increase was announced by the Bureau of Reclamation.

Ultimately, the purpose is not merely to add more water to the stream. It is to create conditions that are less favorable for the rapid spread of disease among adult migrating fish.

In addition to creating better conditions for migrating fish, using stored water above Lewiston Dam offers another benefit.

Managers are able to control both temperature and flow conditions below the dam while salmon are traveling upstream.

Reservoir water provides another option

Using stored water from Trinity Reservoir will be crucial for this effort. Approximately 35,000 acre-feet of water is expected to be used from Trinity Reservoir.

Currently, Trinity Reservoir contains sufficient amounts of stored water so that managers can take advantage of this option.

The reservoir is filled at 109 percent of its historical average for this time of year. As a result, managers can maintain sufficient stored water for additional releases without impacting other obligations.

Monitoring guides the next phase of releases

River conditions will continue to be monitored during this migration period. Agency officials, fisheries biologists, tribal partners, and other interested parties will monitor river conditions throughout the process.

If needed, increased water releases could continue until September 21.

Daily flows would range from approximately 1000 cfs to as much as 1200 cfs during this period.

The additional releases are intended to help salmon move through a critical stage of their migration under more favorable conditions. Managers hope the temporary increase will reduce environmental stress before the fish continue upstream to spawn.