Eurasian Watermilfoil (Myriophyllum spicatum or spiked water-milfoil) is a non-native aquatic plant introduced to eastern North America in the late 1800s. Over time the plant was spread from lake to lake and through waterways, and was first documented in Cultus Lake in the 1970’s. It now covers most of the shallow area of Cultus Lake, with the last estimation covering more than 30 hectares.
Control of Eurasian watermilfoil impacts the health and safety of Cultus Lake aquatic life. The plant has wide-reaching impacts on shallow water fish, insect communities and water quality. It adversely affects sockeye by decreasing the available spawning habitat and reduces oxygen-rich stratum in the water vital to all fish. A known threat to juvenile sockeye in the lake is the northern pikeminnow, a native fish. Eurasian watermilfoil may extend the rearing habitat of pikeminnow, likely increasing predation pressure on sockeye juveniles.
This invasive plant can outcompete and replace native plant communities, reducing overall biological diversity and reducing water quality.
Eurasian watermilfoil inhibits the flow to waterways, irrigation ditches, and drainage canals, where it has the potential to increase maintenance costs. Plants form thick, underwater stands of tangled stems and vast mats of vegetation on the water’s surface. Not surprisingly, the presence of Eurasian watermilfoil has a detrimental impact on recreational activities in the lake as well. These mats can limit human recreation, such as boating, swimming and fishing.
How It Spreads
(Invasive Species Council)Eurasian watermilfoil has spread mostly through human activity, hitching a ride on boats and motors as they are moved from lake to lake. The aquatic plant breaks easily when pulled, while the motion of boats, people and waves can also fragment the plant. The plant fragments are then scattered around the lake by water currents. When the water temperature is above 10C, the sunken fragments take root.
Attacking the Problem
Previously, tilling Eurasian watermilfoil was considered practical in Cultus Lake. Rototilling removed the upper five feet of the plant and has been used in limited areas. While this results in clear swimming spots it also creates fragments that allow the weed to spread. Other methods include waders or scuba divers carefully hand pulling the entire plant and root. Evaluation of this work is ongoing. Another method that has shown some promise is to lay down non-biodegradable mats to smother the plants.
How You Can Help
One of the best methods to help control the Eurasian watermilfoil is to use diligent prevention habits. These include: