[Carry_Okie]

Last century, the Tahoe basin was allowed to burn. A young forest developed in the wake. Young forests consume nitrates. The lack of nutrient turned the lake blue.

Because of fire suppression, that forest is now overstocked and decadent, now releasing far more nitrate into the lake than do anthropogenic sources. Unless that forest is thinned, the cycle will repeat. In many places it's too late: beetle kill and water competition has produced rotting vegetation that releases into watersheds as detritus loaded with nitrates.

[SierraWasp]

"...that releases into watersheds as detritus loaded with nitrates."

Well, let me ask you. What about all the rivers of pine pollen that is loaded with proteins washing into all the storm drains and stream beds and then into the lake?