An ongoing battle

With spring (hopefully) just around the corner and boating season not far behind, the Sanders County Aquatic Invasive Plants Task Force continues to study and work to decrease the aquatic invasive species in the Noxon and Cabinet Gorge reservoirs.

The task force was formed in 2008 after Eurasian watermilfoil (EWM) was discovered in Noxon Reservoir in 2007. Initially, 247 acres of dense EWM in Noxon and 117 in Cabinet were found, and the plant was spreading at a rate of 9.8 percent a year, according to Kim Bergstrom, Task Force facilitator. Through 2016, efforts were made to manage EWM. Those included herbicide treatments and hand pulling, monitoring surveys of the reservoirs, education and outreach, and state-operated boat check stations.

Bergstrom said that between 2012 and 2016, an average of 130 acres were treated each year in Noxon. She said that results looked promising as surveys indicated a decline in dense EWM beds from 247 acres in 2007 to fewer than 10 acres in 2014. She said that if left untreated, "we could have expected more than 400 acres of dense EWM in Noxon in 2014, and more than 700 acres in 2017. The decline in acreage of dense EWM was a direct result from good control achieved from herbicide treatments, which averaged about 90 percent effectiveness per plot."

Bergstrom said plants need to be actively growing for the herbicides to be effective. They wait until water flows have normalized after spring run-off, then have to meet public notice requirements before beginning treatments. She said that typically, that means that treatment will happen in August.

The herbicides are delivered through nozzeled hoses that are extended into the lower portion of the water column so that the herbicide is incorporated into the portion of the water column least impacted by currents, wind and wave action. Applicators use sonar and GIS information to guide delivery of herbicides through the treatment plots.

However, 2015 was a different story, according to Bergstrom. "Due to extremely low runoff and very high temperatures that began in the spring and persisted into the fall, explosive growth of EWM was experience not only in Noxon and Cabinet, but in the entire region," she said. "At that same time, we discovered that a hybrid strain of watermilfoil (HWM) existed in the system, one which appears to be more resistant to herbicides than pure EWM."

With that, the task force took a step back in 2017 to determine the most appropriate approach for treatment. The task force commissioned an independent consultant to perform an Analysis of Treatment Alternatives for invasive watermilfoil. The project wrapped up too late in 2017 for herbicide treatments to be conducted and useful, so no treatments were done. However, Bergstrom said these priority areas were surveyed and mapped by Water and Environmental Technologies in early fall 2017 so that we can prepare for 2018 treatments. A panel of scientific advisors will help determine the treatment protocol for 2018 and give the new priorities and available data on effectiveness of various chemicals and protocols on EWM and HWM. Treatments are planned for mid- to late-summer.

About 1,800 acres in Noxon and 1,100 acres in Cabinet Gorge could support problematic levels of EWM as these are shallow areas conducive to plant growth, according to Bergstrom. If EWM is allowed to persist, she said it can affect habitat for fish, waterfowl and other wildlife, can impede recreation activities, hydroelectric projects and water delivery, and also can block sunlight from penetrating the water column, shading native vegetation.

Another way to combat invasive plant species is with boat check stations. A station near the rural fire station outside of Thompson Falls is operated by Montana Fish, Wildlife & Parks (FWP). Bergstrom said that preliminary 2017 figures show about 4,200 inspections completed at the Thompson Falls station, with about 56 failures.

"Most failures were due to vegetation found on boats, motors and trailers, or there was standing water in vessels," said Bergstrom. "To stop the spread of EWM, mussels and other invasive species, it is very important that boaters inspect, clean, drain and dry their boats, motors, trailers, live wells and ballast tanks every time they take them out of the water."

Bergstrom said there are also check stations in Ravalli, near Troy at the junction of highways 56 and 2, and in Clark Fork, Idaho.

"While the percentage of people we talk to that are aware of EWM has remained very high, the percentage that can actually identify it has grown," Bergstrom said. "However, we get mixed responses related to actions boaters take to inspect their vessels, so will continue to spread the word about how important it is for each recreationist to do their part to help prevent the spread of aquatic invasive species."

Bergstrom said that the task force will work with citizens to combat invasive plant populations near private docks. She said that the Noxon-Cabinet Shoreline Coalition is a voting member of the task force and "is very well represented. The Coalition manages a bottom barrier program for shoreline residents to help get bottom barriers in around private docks. A new development this year, shoreline residents are allowed to remove the invasive plant populations adjacent to their property as a means to provide continued access."

While the eradication of invasive watermilfoil in the Noxon and Cabinet reservoirs is very unlikely, Bergstrom said the program aims to manage the plants at a level that sustains a healthy aquatic environment supportive of native plant populations, fisheries, wildlife, water quality, recreation and local economies.

"This, of course, depends on continued support from our local, state and federal partners both in concept, practice and financially," she said.

The biggest challenge with the aquatic invasive plants management program – other than curve balls such as hybrid strains – is funding. "While we were fortunate to receive state and federal support financially in the early years, the recent discovery of invasive mussels in Montana and recent set-backs due to hybrid species and the 'perfect storm' have made it much more difficult to secure funding," Bergstrom said. "Avista and their Management Committee partners have been strong supporters in the effort to manage EWM all along through allocations from the Clark Fork Settlement Agreement under their operating license, and we hope for that support to continue."

Through 2016, about 60 percent of funding, or $1.5 million, has been secured through state and federal grants, while Avista and a few other sources have contributed $1 million. Bergstrom said there are dozens of task force members who work closely with FWP and the Department of Natural Resources & Conservation, and they work hard to stay abreast of new research and information to use in the local efforts.