SAN JUAN, Puerto Rico (AP) — A popular lagoon that glows at night off Puerto Rico's northeast coast has lit up once again as scientists wrap up their investigation into why it went dark last month, officials said Friday.
A prolonged and heavy swell had swept away microscopic plankton known as dinoflagellates that are found in heavy concentrations in the lagoon and emit light through a chemical reaction when disturbed, said Carmen Guerrero, secretary of the Natural Resources Department.
There are typically thousands of dinoflagellates per liter (gallon) of water in the lagoon, but those concentrations had dropped to less than 100 in early November as heavy swells dispersed them, she said.
"The big swell prevented these organisms from staying in the lagoon," she said.
Scientists found that the swell was eight times bigger than what the lagoon experiences on average.
The lagoon draws hundreds of tourists a year who rent kayaks or boats by night from the nearby city of Fajardo to observe the water emit a greenish light when fish swim by or when they trail an arm through it.
Scientists and residents were concerned that the lagoon stopped glowing because of runoff from the construction of a nearby water and sewer treatment plant, or because of people cutting down mangroves to allow larger boats into the area.