Evaluation of water quality projects in the Lake Tahoe basin.

Lake Tahoe is a large sub alpine lake located in the Sierra Nevada Range in the states of California and Nevada. The Lake Tahoe watershed is relatively small (800 km(20) and is made up of soils with a very low nutrient content and when combined with the Lake's enormous volume (156 km(3)) produces water of unparalleled clarity. However, urbanization around the Lake during the past 50 yr has greatly increased nutrient flux into the Lake resulting in increased algae production and rapidly declining water clarity. Lake transition from nitrogen limiting to phosphorous limiting during the last 30 yr suggests the onset of cultural eutrophication of Lake Tahoe. Protecting Lake Tahoe's water quality has become a major public concern and much time, effort, and money has been, and will be, spent on this undertaking. The effectiveness of remedial actions is the subject of some debate. Local regulatory agencies have mandated implementation of best management practices (BMPs) to mitigate the effects of development, sometimes at great additional expense for developers and homeowners who question their effectiveness. Conclusive studies on the BMP effectiveness are also expensive and can be difficult to accomplish such that very few such studies have been completed. However, several project evaluations have been completed and more are underway. Such study usually demonstrates support of the project's effectiveness in decreasing nutrient flux to Lake Tahoe. Here, we review the existing state of knowledge of nutrient loading to the Lake and to highlight the need for further evaluative investigations of BMPs in order to improve their performance in present and future regulatory actions.