Herbicides, mechanical removal proposed for Beaver Lake milfoil

Montana Fish, Wildlife and Parks has released a plan to remove Eurasian watermilfoil from Beaver Lake.

The draft environmental assessment includes two alternatives to deal with the invasion of watermilfoil in the lake west of Whitefish.

The proposed action calls for eradication of the watermilfoil through a combination of treatments including barrier mats, mechanical removal and herbicide treatment. A no-action plan is also included and could close the lake to boating to minimize further distribution of the watermilfoil. However, the watermilfoil would not be treated under that alternative.

A 25-by-25 foot patch of Eurasian watermilfoil was found near the boat ramp at Beaver Lake last fall. Barrier mats were placed on the weeds to limit growth and control further expansion in the lake. Watermilfoil roots itself to the bottom of water bodies and forms dense mats at the water surface, crowding out native plants and interfering with boating, swimming and fishing.

Beaver Lake is the only known water body in the Flathead infested by watermilfoil. The aquatic invasive species spreads by stem fragments and seed. It grows as water temperatures rise in summer.

A group of state agencies, FWP, the Department of Natural Resource Conservation and Department of Agriculture are proposing to manage and if possible eradicate the noxious aquatic weed from the lake. Funding of $9,000 would come from the DNRC.

Under the no-action plan, the EA notes that without treatment the watermilfoil may spread in Beaver Lake or to other water bodies resulting in loss of native plant species and recreational opportunities. Cumulatively these impacts could be significant due to the limited known distribution of watermilfoil in northwestern Montana, the report says.

Under the proposed action a combination of methods would be used to treat and possibly remove watermilfoil from the lake. Barrier mats will be used to prevent light form reaching the plants in the infested area. Mechanical removal would entail the use of diver dredges to suction plants from the sediment and water. Herbicides would also be applied to the infested area.

The EA notes that there will be minor impacts to water surface quality with the use of herbicide treatment and mechanical removal. The impacts can be mitigated by following specifications for application of the herbicide and using a licensed applicator and curtains to limit spread of the herbicide.

The use of barrier mats and herbicides could impact aquatic vegetation. Areas treated would be limited to infestation and allowing native plants to grow into the treated area would mitigate impacts.

For safety reasons, the water would be closed to use for short periods of time during treatment.

In 2011, mechanical removal of the watermilfoil was attempted, but did not completely remove it as observed by divers this spring. Barrier mats were placed in the infested area last year.

A comprehensive survey of Beaver Lake is expected in late June or early July to determine the distribution of the watermilfoil. Further work to remove the weed is estimated to begin mid-July with completion set for Nov. 1. Monitoring and additional treatments could occur over a five-year period.

Beaver Lake remains open, but there may be closures associated with control actions. Folks are advised to avoid the infested area near the boat ramp, which has been designated by buoys and signs. All boats should be clean, dry and inspected before and after being launched in Beaver Lake.

To review the draft EA visit http://fwp.mt.gov/news/publicNotices/environmentalAssessments/restorationAndRehab/pn_0107.html. A hard copy can be obtained by calling FWP at 752-5501.

FWP is taking public comment on the EA through July 3 at 5 p.m. People can comment on the EA by email: at: mdeleray@mt.gov; or mail to: Mark Deleray, FWP, 490 North Meridian Road, Kalispell, MT, 59901.