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.

If you dive the Marine Room regularly, you already know the drill. Some mornings you wade in off the sand and can see clear across the flats. Other mornings you put your face in the water and can barely see your own hand. Same beach, same short walk from the car, completely different day. I get asked all the time whether the brown water is runoff, the tide, or the swell. At the Marine Room it is almost always the swell, and once you understand how it works you can tell what y

If you have walked a Southern California beach this week, you may have seen it: a sea lion hauled out well above the waterline, head weaving, unresponsive or, worse, thrashing in a seizure. Dead and dying dolphins have shown up on the sand too. This is not random. It is a harmful algal bloom, and the toxin behind it - domoic acid - is worth understanding before your next dive.

The tropics are awake. Tropical Storm Iselle, the first named eastern-Pacific storm to matter for us this season, is pushing a south swell toward Southern California mid-week. It is not a giant - the forecast is a modest mid-period pulse, roughly chest-to-head-high at exposed south-facing breaks, building Tuesday, peaking Wednesday, and easing Thursday - but even a modest south swell changes where and how you should dive.

The California spiny lobster opener is roughly six weeks out - it lands in early October. The divers who limit out on opening night are not lucky. They did the work in September: scouting reefs, servicing gear, and dialing their night dives while everyone else was waiting for a calendar square. Here is how to spend the next six weeks so opening night is about bugs in the bag, not troubleshooting in the dark.