The U.S. Coast Guard is continuing its search for Toronto-based environmental activist and filmmaker Rob Stewart in the waters off Key West, Florida, after crew aboard the Pisces reported him missing Tuesday evening.

Stewart, 37, had been scuba diving near the Alligator Reef by the village of Islamorada on Lower Matecumbe Key when he disappeared.

A coast guard official at the Key West emergency centre confirmed to Playback there have been no sightings or updates since the search began yesterday. A combined surface and air rescue mission, which includes helicopters, fixed-wing craft and search boats has been deployed following the distress call, which was made just before 5:15 p.m. on Jan 31.

One of the crew about the Pisces told coast guard officials that he spotted Stewart shortly after he was reported missing. He has not been seen again.

Friends of the missing director have set up a GoFundMe site to raise funds for rescue efforts and are appealing for divers with deep-water expertise and people with access to boats to join rescue efforts. Over $26,000 had been raised on the site by late Wednesday morning.

Stewart is best known for his 2006 documentary Sharkwater, which established him as an environmentalist filmmaker raising awareness the importance of shark preservation. The documentary, which explores negative human attitudes towards sharks won numerous awards, including the Directors Guild of Canada award for best documentary,  and has been hailed as a seminal conservation film. His second film Revolution (2012) explored ways in which young conservationists around the world are working to save the environment.