Lake Tahoe is an ecological gem and major tourism hub in the Sierra Nevadas, visited by over 3 million people yearly. But, it is under a growing threat from the spread of invasive species: Asian clams, Largemouth Bass, Eurasian watermilfoil and curly leaf pondweed are already well-established. These species are changing the lake’s ecosystem, concentrating nutrients, causing algae blooms and creating habitat for other invasive species, such as goldfish and bass. These species also cause shoreline degradation, impacting how people can vacation on and use Lake Tahoe. Further environmental degradation is not only undesirable in and of itself, but could have serious economic impacts on the region.

Aquatic resource managers for the Lake need to have a way to easily track these species, so they can mitigate further spread and associated damage. To help them with this, SIG prepared a 2018 status report for aquatic plants, and prepared and implemented a monitoring and evaluation plan for Lake Tahoe invasive species. The monitoring plan included the protocols and detailed information required to consistently collect, quantify and report on the status and change in composition, relative abundance/density, distribution, and extent of native and aquatic invasive plants.

Because of the large area (i.e., lake-wide) that needed to be monitored, and the fine-scale resolution needed to detect change in the lake, SIG scientists used different remote sensing platforms, including manned aircraft and unmanned aircraft systems (UAS) that collected LiDAR data and high-resolution 4-band imagery. The UAS data was used to generate seamless, high-resolution color geo-referenced mosaics, and, where possible, digital elevation datasets to prepare the status report. Maps of aquatic plant species were then validated through diver surveys, and the data was further used to train mapping efforts.

By using of a variety of acquisition methods, SIG kept monitoring costs down and met project objectives. Aquatic resource managers also now have an accurate baseline from which to monitor the spread of aquatic plants, and a plan for how monitor them in the future. Lake Tahoe managers have been working diligently for decades to stop invasive species – having more tools in their toolbox will help them protect the lake for future generations, and keep lake tourism thriving.