Algal growth at Lake Tahoe has shifted from frequent stimulation by nitrogen to stimulation by phosphorus.
Excessive atmospheric deposition of atmospheric nitrogen meets the algae's needs for this nutrient. Thus phosphorus has become the limited nutrient needed for algal growth. Since phosphorus is typically transported into the Lake with sediment, controlling algal growth means controlling sediment flow, mitigating erosion, acquiring of sensitive lands, treating surface runoff and performing other restoration efforts.

Five sources of nutrients into Lake Tahoe have been identified; (1) direct atmospheric deposition and precipitation, (2) stream discharge, (3) overland runoff directly to lake, (4) groundwater and (5) shoreline erosion.
The major losses of nutrients from the Lake include the settling of material from the water column to the bottom and, to a much lesser extent, discharge into the Truckee River. Phosphorus (P) and nitrogen (N) loading (the total amount of each nutrient in the lake), expressed as metric tons per year, were largely determined using long-term data collected as part of the Lake Tahoe Interagency Monitoring Program. These results are preliminary.

Direct runoff, stream loading and atmospheric deposition account for approximately 35%, 30% and 25-30% of the nutrient load, respectively. Annual loading of total phosphorus into Lake Tahoe was estimated to be approximately 46 metric tons.
This suggests that the three important sources of phosphorus should be evaluated in more detail to determine the specific sources of P within each category, and to evaluate the cost-benefits for P-reduction within each. Of the estimated 418 metric tons (MT) of nitrogen loaded during a representative year, over half (56%) comes from direct atmospheric deposition on the lake surface. Direct runoff, groundwater and stream loading contribute on the order of 10%, 15% and 20%, respectively.

Estimates suggest that approximately 15 MT or about 30-35% of the total-P load is in the soluble-P form.
Soluble-P is immediately available to organisms and can therefore have a substantial impact on an ecosystem. Managing soluble-P is critical to the health of the Lake.

Analysis of material contained in a vertical series of sediment traps deployed in Lake Tahoe, independently shows that nutrient sedimentation losses to the bottom of Lake Tahoe are 401.7 MT for total nitrogen and 52.8 MT for total phosphorus.
These measured values agree remarkably well with the independent loading estimates given above. Loss of P and N via the lake's only outflow is minimal. This close agreement give us increased confidence that the loading rates are representative.