In the News

Removing the Invasive Aquatic Weed: Eurasian Watermilfoil
date posted: December 1 2005

Lake Tahoe Report #124
July. 5, 2005
By Heather Segale and John Cobourn

Many Lake Tahoe boaters have heard of Eurasian watermilfoil (Myriophyllum spicatum), an aquatic invasive weed that has been spreading around Lake Tahoe’s shoreline since 1992. A survey completed in 2003 found that it is rapidly expanding along the western end of Emerald Bay, and has now colonized most marinas and some protected coves and beaches.

Eurasian watermilfoil is not native to the area. It has spread throughout the United States and become firmly established in the West. Once established, it degrades fish habitat, fouls boat propellers, chokes out native plants, and accelerates algae growth, a contributing factor to the decline in lake clarity.

Eurasian watermilfoil is very difficult to control. It has become a major headache in local marinas, such as the Tahoe Keys, costing tens of thousands of dollars each year to control. Marinas typically use mechanical harvesters to mow the weed below the water’s surface. The removal process creates plant fragments that can attach to boat parts or drift to new locations and establish new plant colonies. Therefore, mechanical harvesting actually can accelerate the spread of milfoil to other areas of the lake. Recently, the California State Lands Commission investigated the status of milfoil in the lake, reported to be expanding at several sites, and found that the potential for continued spread of this species is increasing due to the current management strategy in South Lake Tahoe.

Since chemical treatments, or herbicides, are not allowed in Lake Tahoe, it can be very costly to control this weed. Its further expansion increases the potential for major, long-term, adverse, environmental, recreational and aesthetic impacts to the lake. Local resource agencies have not yet developed a comprehensive plan to control the spread of milfoil in the lake.

However, there is hope. The California State Lands Commission recently conducted a pilot project to remove Eurasian watermilfoil from Emerald Bay. They hope to demonstrate the effectiveness, of using divers to hand-remove the plants, assisted by vacuum suction. This pilot project will provide valuable information to resource and water quality managers and assist in the development of an environmentally sound plan for the management of Eurasian watermilfoil in the lake.

Last month, the California State Lands Commission, along with a dive crew from Aquatic Consulting and Evaluation, surveyed Emerald Bay and removed milfoil for three days. They used a suction device to prevent the fragments from escaping. One diver pulled plants, and a boat crew collected the plants and any fragments with a dip net. They were able to remove 65 pounds of fresh weight milfoil.

This team plans to come back in September to measure and weigh any milfoil that they missed. They hope to knock the milfoil down to a small infestation that can be easily controlled. If it is determined that this control regimen is effective, they can begin work on other areas around the lake.

What can you do? As with most exotic or nonnative plants, the best approach is to prevent invasion. Once an invasive species is established, complete eradication is highly unlikely. However, there are some ways that visitors and residents can help:

•When leaving infested areas, boaters should stop and run the engine in reverse to knock plant parts off the propeller to avoid spreading fragments to other locations.

•Check boats, trailers, and all other watercraft for aquatic plants before launching them and after leaving any body of water. Check the propeller, air intakes, tires, etc. Remove aquatic plants, place them in a plastic bag, and put the bag in a garbage can.

•Tell friends and neighbors so they can help control this weed.

For more information, contact Kim Melody, invasive weed outreach coordinator, Tahoe Resource Conservation District, (530) 543-1501, ext.111.

Watch for the “Lake Tahoe Report” in the Tahoe Daily Tribune each Wednesday, and tune in to KOLO-TV News Channel 8 Tuesdays at 5 p.m. to learn more. The “Lake Tahoe Report” is a collaborative effort of the Lake Tahoe Environmental Education Coalition, University of Nevada Cooperative Extension, UC Davis Tahoe Environmental Research Center and the California State Water Resource Control Board. For more information, contact Heather Segale, UC Davis Tahoe Environmental Research Center, (530) 583-3279, or logon to www.lteec.org or www.tahoe.unr.edu.