SAN DIEGO (AP) — A red tide is causing the surf to glow in parts of California.

An algae bloom filled with bioluminescent phytoplankton has been lighting up the ocean from La Jolla to Encinitas since Monday. It’s a stretch of about 18 miles (29 kilometers). The micro-organisms light up along the face of the wave when it crashes near the shore.

Oceanographer Michael Latz tells The San Diego Union-Tribune the last red tide was in September 2013. He says scientists can’t predict when they’ll occur and they really don’t understand the dynamics.

[cover photo Phil Gibbs via Flickr]