Ecological Conditions and Aquatic Invasive Plants
The Tahoe Keys lagoons are located on the south edge of Lake Tahoe in the City of South Lake Tahoe. The Tahoe Keys and surrounding lagoons were constructed in the 1960s on the Upper Truckee River Marsh by excavating the lagoons and capping the soil with sand to form stable building sites. The development includes 1,529 homes and townhomes, 900 docks, a commercial marina, and a commercial center. Three primary man-made water features exist in the Tahoe Keys:
- Main Lagoon (also known as the West Lagoon)
- Marina Lagoon (also known as the East Lagoon)
- Lake Tallac Lagoon
These three water features are referred as the “Tahoe Keys lagoons” and encompass 172 acres of waterways.
The excessive growth and expansion of aquatic weeds in the lagoons is due to several environmental conditions including abundant nutrient availability, and relative warm, stagnant and shallow waters with sufficient light for weed growth. The target aquatic weeds introduced to the lagoons have found ideal habitat conditions for prolific growth.
While the shallow, warm waters of the Tahoe Keys lagoons create conditions favorable to the growth of aquatic weeds, boats are the primary vectors by which they are spread to areas around greater Lake Tahoe. The first invasive plant, Eurasian watermilfoil (Myriophyllum spicatum), became established in the 1980s and 1990s, and curlyleaf pondweed (Potamoeton crispus L.) was discovered in Lake Tahoe in 2003.
This second non-native, invasive weed is of particular concern due to its recent rapid growth and spread, with the potential to infest more of Lake Tahoe’s aquatic habitat than Eurasian watermilfoil. Curlyleaf pondweed is more difficult to control due to the size of infestations and multiple methods of plant propagation – via seeds, plant fragments and the production of turions – wintering buds that become detached and spread throughout the waterway and have the potential to remain dormant at the bottom of the water for several years. In addition, it has the capability to grow in deeper, colder waters, making curlyleaf pondweed potentially detrimental to Lake Tahoe if allowed to spread unchecked (Woolf and Madsen 2003, UNR 2015, Xie and Yu 2011).
The plant’s swift and multiple modes of establishment, coupled with its ability to tether to boats, strongly suggest that this invasive species could become well established in much of Lake Tahoe’s nearshore – depths of 30 feet and less – within the next few years.
Currently, curlyleaf pondweed is limited to the south and southeastern shores of Lake Tahoe with infestations observed from Taylor Creek to Lakeside Marina (Wittmann and Chandra 2015, LTSLT 2016). Newer infestations were recently found as far north as Elk Point Marina (Anderson 2016, pers. communication) on the Nevada side of Lake Tahoe.
The two invasive, non-native aquatic weed populations in the Tahoe Keys have been growing rapidly. Recent aquatic plant surveys (2014, 2015, 2016, 2017) show the extent and density of excessive plant growth in the lagoons. In recent years, 85% to 90% of the available wetted surface in the lagoons has been infested with target aquatic weeds with a large majority being the non-native invasive species.
A third target weed, Coontail (Ceratophyllum demersum), is classified as a native plant to California, but in recent years has grown in abundance in the Lake Tahoe region, specifically in the lagoons. Coontail has heavily infested the deeper channels of all the lagoons, most abundantly in the Marina Lagoon and Lake Tallac Lagoon, where it comprises over 70% percent of the aquatic plant matter (TKPOA 2016a).
Threats to Water Quality and Use