My guess is that the pollen count is pretty steady, regardless of the condition of the forest, compared to the difference between a young forest after a fire versus a decadent forest full of rotting biomass. There may be a lot of pollen, but given the historical data the lake can clearly handle that amount.
I mean there's the golf course fertilizers that feed the algea that everybody keeps screaming about as a token of all the dastardly development by greedy capitalistic devilish developers/speculators for fun and profit in the evil America that allows such sport at the expense of the fragile, pristine environment!!!(dripping sarcasm in response to a total overload of militant environmentalistic rhetoric for the past 40 years)