FWP warns St. Mary Diversion problems could impact fisheries

Montana Fish, Wildlife and Parks warned Tuesday in a story in its newsletter that the collapse of part of the St. Mary Diversion and Conveyance Works could have an impact on fishing in the area.

“Montana Fish, Wildlife and Parks is working with BOR to monitor this situation and its potential impacts to Fresno and Nelson reservoirs and the Milk River drainage,” the story says.

Work is underway to repair the structure that collapsed, Drop 5 near the end of the 29-mile system of dams, dikes, canals, gigantic metal siphons and concrete drop structures, as well as another structure, Drop 2, that was regarded as in danger of catastrophic failure.

Work on Drop 2 was planned for this year, and the work on Drop 5 was added after it failed May 17.

U.S. Sen. Steve Daines, R-Mont., brought Department of Interior Assistant Secretary for Water and Science Tim Petty to Montana Monday to tour the diversion, built more than 100 years ago to divert water stored behind Sherburne Dam on Swift Current Creek, into the Milk River, and to hold a roundtable discussion of the issue in Cut Bank Monday afternoon.

The diversion was built by Bureau of Reclamation as part of the irrigation system the Milk River Project, and also is used as a municipal water source by towns including Havre, Chinook and Harlem, and provides recreation opportunities.

Daines and Sen. Jon Tester, D-Mont., and Rep. Greg Gianforte, R-Mont., are trying to shift the funding for the system from about 75 percent provided by the users and 25 percent by the federal government so the federal government picks up about 75 percent of the cost of operation and maintenance.

The diversion provides much of the water that flows through the Milk River, which typically ran dry by fall in 6-out-of-10 years before the diversion was built.

The diversion has been shut down since the drop collapsed May 17.

At the time, Fresno and Nelson reservoirs, part of the Milk River Project that use water from the diversion, were at very high levels, but have been drawn down for irrigation use.

The FWP story said that as the reservoirs drop, the fish populations could be impacted, although Nelson is not expected to be effected severely.

Fresno was heavily stocked by FWP last decade after a severe drought that started in 2000 nearly emptied the reservoir at times.

FWP Fish Biologist Cody Nagel told the Havre Daily News said the fish population in Fresno dropped after stocking stopped in 2012, but that was from record levels in 2010 and 2011.

The forage base had stabilized in the last few years and was at nearly ideal levels from the perspective of environmental sustainability, he said.

But the article in the newsletter warned that as the levels drop, that could impact the fisheries.

The article says Fresno Reservoir is projected to be 24 feet below full pool by Aug. 15, and studies have shown that reservoir levels 20 feet below full pool for extended periods of time, especially into winter, can be extremely detrimental to the fish community, the article says.

Nelson Reservoir is projected to drop about 5 feet by mid-August, which will have no significant impact on the fishery, the article says. Nelson fisheries tend to see more significant impacts if the reservoir falls to more than 12 feet below full pool.

Impacts to the river itself depend on how long river sections are dry or see limited flow, the article says, and impacts could be mitigated if heavy summer and fall rains occur.

The article refers people with questions about the Fresno and Nelson fisheries to Nagel at 265-6177 or via email at [email protected].