One of Puerto Rico's three famous bioluminescent lagoons has suddenly and inexplicably stopped glowing. The Bioluminescent Bay in Laguna Grande in Fajardo, on the northeast corner of the island, is a popular nighttime kayaking spot, but the lack of the normal glowing waters over the past few weeks has disappointed tourists and forced park officials to offer refunds. The waters normally glow a green light when they are disturbed, such as when a kayak or other boat moves through them.

Scientists and government officials are trying to figure out why the bay has stopped glowing. "We have been compiling data," Carmen Guerrero, secretary of the Department of Natural Resources, told the Associated Press. "There are a lot of factors that could be at play."

Those possible factors include construction runoff, unusually heavy rains and the removal of local mangroves from the bay. Mangroves supply necessary nutrients to the bay, which help support its unique ecosystem. The mayor of Fajardo blamed the nearby construction of a new sewage treatment plant, something plant officials deny. Ironically, the new sewage treatment plant is being built in part to help preserve Bio Bay. Nonetheless construction has temporarily been halted until scientists can determine why Bio Bay has stopped glowing.

A University of Puerto Rico biologist told the AP that Laguna Grande also almost went dark 10 years ago but bounced back after a few months.

Laguna Grande's bioluminescent properties were first observed way back in the 17th century by visiting Spanish explorers, who called it the "devil" glowing water reservoir. They quickly constructed a small canal which mostly blocked the lagoon from the ocean, enhancing its luminescent qualities. The glow itself is caused by algae that live in the water and glow when they disturbed, much in the same way that fireflies glow in the air.

There are no reports of Puerto Rico's two other Bio Bays – in Vieques and on the smaller island of Lajas – being similarly affected.

You can see the Laguna Grande region and some of the bioluminescence in Bio Bay in this video:

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