'Tis the season for gray whales swimming around the Bay, and windsurfers and kitesurfers can take this as a word of warning to not go barrelling around too fast without knowing how many whales might be in your midst.

Windsurfer Eric Kramers was out for a day of windsurfing last week, and this video, taken from Crissy Field, shows the moment that his board collided with a surfacing gray whale, sending him tumbling off into the water.

"It was a 'whale' of a day," Kramers jokes on Instagram. "Please be cautious and respect wildlife, I had reduced my speed greatly bc I had seen a couple whales in the area but on my last run back it just popped up right in front of me. Glad we are both ok."

The whale appears unhurt, though it's hard to say if the rudder blade of the windsurf board came in contact with the whale.

This collision, while seemingly minor, comes amid a report Monday that there have now been four gray whale deaths in the Bay since the start of the year, with two found dead just this past weekend.

As KRON4 reports, a deceased adult female gray whale was spotted floating off Tiburon near the Larkspur Ferry Terminal, and its cause of death has not yet been determined. Another dead whale was reportedly spotted near the Point San Pablo Yacht Harbor, however researchers at the Marine Mammal Center have not yet been able to locate it.

Gray whale deaths have been a relatively frequent occurrance in the Bay in recent years, with the causes determined to be primarily ship strikes, and malnutrition. The phenomenon of gray whales — and, sometimes, humpback whales — entering the Bay appears linked to food supplies, with some whales likely remembering, from recent years, that they can find sustenance in the Bay during their annual migration to Alaska for the summer.

Last year, the largest number of gray whale deaths in 25 years was tallied in and around the Bay, with 21 total dead whales found between March and July. This was after 35 confirmed sightings of gray whales in the Bay throughout the season, which itself was an unusually high number.