Aquatic Invasive Plants

Eurasian watermilfoil (Myriophyllum spicatum) is an attractive plant with feathery underwater foliage and was once sold as a common plant for aquariums. It is thought to originate in Europe or Asia and was most likely introduced to Lake Tahoe in the late 1960’s to early 1970’s; at the same time the Tahoe Keys housing and marina were developed. Once established, milfoil can drastically alter a water body. It creates very dense mats of vegetation on the surface of the water that interfere with many recreational activities and if left unchecked, can ultimately interfere with water intake structures.

Curlyleaf pondweed (Potamogeton crispus), also a popular aquarium plant originating from Eurasia, Africa and Australia is also dispersing and establishing new colonies within the Tahoe Keys and along Lake Tahoe’s south shore. Curlyleaf pondweed is considered a deep water plant but can colonize in shallow water as well. This plant can tolerate extreme conditions including low light and cold water temperatures. It grows actively during winter months when most plants are dormant, reaching the peak of its growth season in summer. Although the plant provides habitat during the winter, decay in the summer causes nutrients to be released into the water which can trigger algal blooms.

The largest concentration of watermilfoil within Lake Tahoe occurs in the Tahoe Keys. This plant, however is continuing to disperse and establish new populations around the lake. Curlyleaf pondweed was initially documented in the Tahoe Keys entrance channels in 2003. New colonies have spread eastward with the densest concentrations now occurring at Ski Run.

Invasive aquatic weed work in the Tahoe Keys is a key component of the strategy to attack both source and satellite invasive weed populations. During fiscal year 2009, a study plan was developed for “Evaluation of Methods for Aquatic Invasive Species Management in the Tahoe Keys” by Dr. Lars Anderson, US Department of Agriculture, Agricultural Research Service. The Lake Tahoe Aquatic Invasive Species Coordination Committee has been working with the California Water Quality Control Board, Lahonton Region, to allow the limited use of qualified, tested herbicides in a controlled and confined manner in the Tahoe Keys lagoon area to control invasive weeds.