If you dropped into Shaw's Cove this week and thought the bottom looked... different - lower, rockier, more reef than you remembered - you're not losing your mind. The big south swell that ran through over Labor Day did what big swells do: it grabbed the sand and moved it. Here's what happened, why it happens, and what it means the next time you gear up.

Over Labor Day weekend, the leftovers of Hurricane Marie threw a giant south swell at Southern California, and the whole coast felt it. The storm itself never came close - it stayed 700-plus miles to the south and west - but the long-period energy it fired off put High Surf and Coastal Flood advisories on the map through Tuesday, and set off a chain reaction that touched water temperature, visibility, the shape of our favorite coves, and even what showed up on the reef.

The thermometer just dropped, and if you dive San Diego you should be paying attention - because a cool-down like the one we just had is exactly the kind of switch that wakes up white seabass. After a summer of warm, lazy water, the ghosts of the kelp are back on the menu. Here's how to be ready.

The swell that worked Southern California over the holiday weekend - Saturday through today, Monday, September 7 - was a strong south to south-southwest swell thrown off by Hurricane Marie. What made it worth writing about was not the size so much as how directional it was. Some beaches got hammered while a cove a few hundred yards away sat almost calm. That is the whole story of this swell, and it is a good lesson in how to read a south swell as a diver.

It is Labor Day weekend, and the water is doing exactly what you would expect for early September - warm, blue offshore, and worth the effort if you pick your spot. The late-August blow that browned out the coast has settled down, the diving is coming back, and the warm water has the coast loaded with fish worth putting a shaft in. It is also one of the busiest boating weekends of the year, so staying visible and staying safe in heavy boat traffic needs to be front of mind. H

September is the month that usually rewards patience. The water stays warm, the crowds thin out after Labor Day, the wind lays down in the mornings, and the swell windows get longer. It is, in a lot of years, the single best diving month on the California calendar. Here is how the month is shaping up and where the opportunities are.

This is what actually happened in the water in August, region by region, grounded in dozens of in-water reports and the offshore intel that shaped the month.

You have probably seen the map going around, the one with the big orange arrows pushing warm water up the California coast and a bunch of sharks and sea snakes riding along with it. It looks dramatic, and honestly the basic idea is real. A strong El Nino warms up the eastern Pacific, and that warm water pulls a lot of southern species north with it. Some of that is great news for us as divers.