Milfoil Control

Program Information

The spread of the non-native aquatic plant Eurasian Water Milfoil (Myriophyllum Spicatum L.) in the lakes of the CSRD is a continuing problem.  Aquatic plants are in most cases, an important component of any lake's environment.  However, they can also have undesirable effects when they are too abundant or growing in the wrong place.  Dense mats of surfacing milfoil can adversely affect recreational activities such as swimming, boating, water-skiing and fishing. Luxuriant growths 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. During the spring and summer, rapid growth from the root crown area produces reddish shoots that grow to the surface where emergent stem tips flower. Milfoil propagates and 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. New plants grow when the fragments drift ashore and sink during the spring and summer months. Favoured sites for colonization are backwaters and areas of recent bottom disturbance. 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 the 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% 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.

Future plans for Eurasian Water Milfoil control include continued research into biological control methods and further development of mechanical treatment techniques.

Prevention

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

You can help prevent the spread of Eurasian Water Milfoil by being very careful not to transport pieces of milfoil from one water body to another and by reporting new sightings in non-infested lakes. Milfoil can stay alive for weeks if they remain wet and removal before entering another water body is necessary to help prevent the spread of this invasive plant.

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

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