Weed killing mats lining parts of Lake Tahoe

The final bottom barriers have been installed at Lakeside Marina, completing a project to cut light to invasive weeds that thrive in warmer parts of Lake Tahoe.

With boat activity and shallower water, marinas are a hotbed for invasive weeds such as Eurasian Watermililfoil (Myriophyllum spicatum) and Curly-leaf Pondweed. If allowed to thrive, the rooted, submerged aquatic plants can grow several feet tall and cause problems in the lake: Affect water recreationists when they grow as a dense mat at the surface; overtake habitat and outcompete native aquatic plants, potentially lowering diversity; and provide unsuitable shelter, food, and nesting habitat for native animals.

The Tahoe Resource Conservation District (Tahoe RCD) had originally planned for five acres of the bottom barrier mats around Lake Tahoe, but they found through pre-season monitoring that, for now, some areas just needed some hand pulling of the weeds or diver assisted suction removal. The mats are made of a gas-permeable synthetic material, so oxygen goes through, but light does not.

Mats have been installed by Tahoe RCD and their partners at Crystal Shores East, West and Villas, Tahoe Vista Boat Launch, Fleur du Lac, and the Truckee River and Dam, as well as Lakeside Marina.

On Tuesday, the last of the Lakeside Marina mats were installed by SCUBA divers with Marine Taxonomic Services. During this process they cut rebar to a certain length, attach caps to the end of each rebar, feed the rebar through the benthic barrier mats at specific locations, and then roll up the bundles of mats in preparation for them to be deployed into the marina. From there, the Marine Taxonomic Service SCUBA diver crew positions the barriers over the weeds in the marina and anchors them down.

The Tahoe Water Suppliers Association (TWSA) issued a matching challenge in June 2017 to help ensure that the remaining bottom barriers could be purchased. With the full inventory of mats, more aquatic weeds will be removed from the Lake and the water quality will be improved. The Tahoe Fund accepted the challenge to help raise over $26,000 to help purchase 175 of the bottom barrier mats. At the time, the inventory of bottom barriers was 1.6 acres short of the maximum five acres of coverage permitted for Tahoe. Every dollar the Tahoe Fund raised was to be matched by the TWSA.

Currently Tahoe RCD holds a Mitigated Negative Declaration for lake-wide Aquatic Plant Control. Permits from regulatory agencies use this document for supporting environmental review. Tahoe RCD has funding to upgrade their current environmental documentation to include other treatment methods including UV light and suction dredging. They hope that through this environmental review process they can increase the overall project acres treated each year. Development of this new document will begin this winter.