I'm not contesting the Everglades' role in filtering nutrients, but consider that the acreage of Glades, mangroves and seagrass are much less than they once were (before we started carving them up), and the nutrients levels they must filter are unnaturally high.
Best as I remember, nitrogen and phosphorus both contribute to algae blooms, and unfortunately, the Everglades Restoration Plan only addresses one of those nutrients. The idea was that by lowering the levels of one nutrient (let's say nitrogen), the occurrence and intensity of algae blooms could be lessened. That might actually work, at least until water not regulated for nitrogen from other sources, like the Mississippi River*, mixes with Everglades water high in phosphorus, and then you still get algae blooms. That was one of the many criticisms I heard about the ERP. Algae blooms aside, factor in that the high-phosphorus water leaving the Everglades flows into Fla Bay and through the Keys (and their corals, which don't respond well to nutrients).
*There are plans for a Louisiana/Miss River Restoration, by the way. And there are efforts focused on a holistic, watershed approach to restoring the Mississippi, the Gulf, the Everglades, and the Caribbean.