Harmful algal blooms (HABs) release numerous toxins that threaten drinking water, food sources, and wildlife. One HAB toxin, the neurotoxin β-methylamino-L-alanine (BMAA), is ubiquitous in ecosystems worldwide. This research evaluates the presence of BMAA and its isomers in organisms in Lake Erie, which experiences seasonal HABs, and assesses the potential for toxin biomagnification. It also characterizes the behavioural effects of chronic exposure to environmentally relevant concentrations of BMAA on larval zebrafish. Results show that BMAA isomers are detected more frequently and at higher concentrations than BMAA itself. Different groups of organisms also show distinct isomer content profiles in their tissues. Environmental concentrations of BMAA have a moderate, dose- and light condition-dependent effect on larval zebrafish activity. Light condition may be an important factor when examining the behavioural effects of BMAA exposure. My results emphasize the importance of considering the species-and isomer-specific toxicology of BMAA in future field and laboratory studies.