Milfoil Control

The spread of the non-native aquatic plant Eurasian Water Milfoil in the lakes of the CSRD is a continuing problem. Dense mats of surfacing milfoil can adversely affect recreational activities such as swimming, boating, water-skiing and fishing. This can also affect flood control, irrigation, drainage, water conservation facilities and fish spawning areas.

Milfoil is a rooted aquatic plant colonizing in the 0.5 meter to 5-meter (18 inches to 16 feet) depth range. Milfoil spreads primarily by stem fragmentation during the active growing season - floating stem fragments broken off the parent plant by wave action or boating activities are spread rapidly by natural water currents or by boat propellers. It takes only one small piece of milfoil to start a new plant which in turn can expand into a very large colony in a short period of time.

History

Eurasian Water Milfoil was first located in the Shuswap Lake system in August of 1981 near the government boat launch in Sicamous. Over the last three decades, milfoil has colonized throughout Shuswap Lake as well as Little Shuswap Lake, Mara Lake and the Shuswap River. The largest infestation is located in Salmon Arm Bay.

Fortunately, the Shuswap system is not yet as badly infested as other lakes in BC, in many cases you may not even be aware of any milfoil plants in the area. The CSRD is working hard to see that it stays that way. The efforts of this program have been successful in reducing the impact of Eurasian Water Milfoil in the Shuswap - in particular, higher elevation lakes such as White Lake.

Survey & Treatment

Surveys are completed on a regular basis using aerial photography or by inspecting and measuring sample sites. These surveys provide information regarding the rate of spread and the effectiveness of completed treatments.

In 1989, the CSRD and the Province of BC jointly designed and constructed a state-of-the-art vessel for use exclusively in the Shuswap Lake system. The orange 41-foot long "MRV Shuswap" can be seen at work during the Autumn and early Winter on rototilling duty.

Timing for the rototilling program is important - the ideal conditions occur when water temperatures reach 10° C or less, when the plant is dormant and any released fragments are not viable. The rototilling process lifts root crowns and plant matter which immediately float to the surface and eventually drift to shore where they dry out and die. The rototilling process is proven to be over 90 per cent effective in reducing plant density.

When other technologies cannot be used to effectively treat a high-recreation use area, an aquatic weed harvester may be used. The harvester is a cosmetic treatment only - it cuts a series of 3.04-meter (10 foot) wide swathes to a depth of 1.6 meters (5 feet) and collects the stems into a series of conveyers. When the machine is full, it unloads the cuttings on shore for collection and disposal. This type of treatment gives short-term relief allowing swimmers and boaters freedom of movement through previously infested areas.

Prevention

As with most invasive plants, once milfoil establishes, it is almost impossible to eliminate. Prevention is the best way to stop its spread.

Before entering the water, inspect and clean your boat, trailer, float tubes and other watercraft. Learn to identify Eurasian Water Milfoil, where it is known to occur and then take all appropriate measures to prevent its spread to other locations.

Other undesirable materials can be moved into lake systems by boats, most notably invasive species of mussels, including Zebra and Quagga Mussels. The CSRD, along with the BC Conservation Office Service and the Ministry of Environment and Climate Change Strategy, is supportive of the Clean, Drain, Dry initiative to encourage boaters to keep their vessels free of these species. Watercraft inspection stations have also been set up in an effort to protect lakes in the region.

Reports

View Milfoil Control Reports.