But the bloom, which extends for nearly 100 miles, does not appear to pose any dangers for people or marine life.
Officials say the bloom appears to be a naturally driven event, with the mass of microscopic plants growing on nutrients pulled up from deep waters by upwelling.
It's the same wind-driven phenomenon of summer that pushes warm surface water away from the beach, leaving swimmers shivering at the nip of colder waters in August.
The bloom is several miles offshore and goes along roughly two-thirds of the New Jersey coastline, from the southern end of Monmouth County to Cape May.
