Dynamics of microcystins and saxitoxin in the Indian River Lagoon, Florida

•The presence of diatoms, dinoflagellates, and cyanobacteria matched observed patterns in microcystins.•The presence of diatoms and dinoflagellates matched observed patterns in saxitoxin.•Observed patterns in toxin concentrations were highly related to dissolved nutrients.•High concentrations of saxitoxin were identified in high N:P environments.•Toxicities to some mammalian cell lines suggest unidentified toxins in the IRL.