It is widely assumed that nutrients in Florida Bay are linked to agricultural runoff. The assumption is easy to understand because, on the surface, there is a freshwater connection between agricultural areas and the Bay.
Water draining off agricultural land obviously carries nutrients in the form of fertilizers.
It's assumed that the runoff finds its way to Florida Bay and fuels the algae blooms. The logic is there, but the findings don't support it. It turns out that the Everglades marsh is very efficient at removing most nutrients from the water. Water drained off agricultural land into the canal system is high in some nutrients. Then, for Taylor Slough and the C-111 basin, the water is either pumped out of the canal, or let out through culverts, into Everglades marsh.