Why San Diego's Water Is So Clear Right Now

Record-warm water has pushed La Jolla visibility to 50-60 feet. Here's what's behind it, how to make the most of it, and what to watch for as El Niño builds this winter.

If you've been in the water off La Jolla this month, you already know. Divers are coming up from Scripps Canyon, La Jolla Shores, and the Marine Room describing some of the clearest water they've ever seen here. Brian Zach, owner of Zach's Scuba Shack, told CBS 8 he's been seeing 50 to 60 feet of visibility, the best in his ten years of diving these sites.

This isn't a lucky week. It's the result of the same ocean conditions making headlines all year: a record marine heatwave off Southern California, with a strong El Niño now building on top of it.

Warm water, empty water

Most of the time, the thing limiting visibility in San Diego is life itself. Plankton, the microscopic plants and animals at the bottom of the food chain, cloud the water column, and they thrive on nutrients carried up from the deep.

That nutrient supply depends on upwelling. Steady northwest winds push surface water offshore, and cold, nutrient-rich water is drawn up from below to replace it. It's why a normal San Diego spring can bring cold, green water that's full of life but hard to see through.

This year, that engine has stalled. Warm conditions have come with light winds, so there's been little upwelling. A thick layer of warm water now sits on top of the ocean like a lid, blocking nutrients from reaching the surface. Fewer nutrients means less plankton. Less plankton means clear, blue water.

"The vis is incredible because the high temp has killed off the plankton."

Bruce HobbaCalifornia State Lifeguard (retired)

Scientists at Scripps Institution of Oceanography describe the same chain of events. Melissa Carter, who manages the Scripps Shore Stations Network, told CBS 8 the warm water "feels amazing" to divers but is "not great" for mixing, nutrients, and plankton. The only comparable October in Scripps Pier's 110-year record was 2015, during the last major marine heatwave and El Niño.

Where to take advantage of it

La Jolla Shores and Scripps Canyon

The canyon walls, sand flats, and the Marine Room reef are where the best visibility reports are coming from. Snorkelers at the Shores have been filming octopus and green sea turtles in water clear enough to see the bottom from the surface. Remember that much of this area is within the Matlahuayl State Marine Reserve, which is no-take: look, film, don't collect.

Point Loma and Sunset Cliffs

Lobster season opened October 2, and clear water makes it a lot easier to spot antennae in the rocks. You'll need a current California fishing license and a spiny lobster report card, filled out as you go. Check CDFW for current size and bag limits before you head out.

Watch for unusual visitors

Warm water is drawing tropical species north. Scripps researchers have noted reports of whale sharks, hammerhead sharks, and other warm-water animals in Southern California this year. Clear water is your best shot at actually seeing one.

The catch: what the clear water costs

It's hard not to enjoy 60-foot visibility in 70-degree water, but it comes at a price for the reef.

• The kelp is disappearing. Giant kelp needs cold, nutrient-rich water and starts breaking down above about 68°F. The thick kelp forest near the quarter-mile buoy off La Jolla Cove is now essentially gone. Scripps kelp researcher Jennifer Smith has reported 70°F water even 50 feet down.
• Less food up the chain. Without plankton, baitfish move offshore or deeper. During the 2014-15 heatwave and El Niño, that food shortage contributed to starving sea lion pups along the coast.
• Fewer fish on familiar spots. With the kelp canopy thinned out, the calico bass, sheephead, and schools of blacksmith that normally shelter there may be harder to find.

Divers can help. Local efforts like Kelp Restoration La Jolla are working on surveys and replanting, and Scripps scientists are studying heat-tolerant kelp from Baja California. Logging what you see, kelp included, helps track how the reef changes.

How long will it last?

Nobody can promise, and conditions can change from one week to the next. NOAA puts the odds of a strong-to-very-strong El Niño this winter at 83%, so warm water is likely to stay. But El Niño winters also tend to bring more storms to Southern California, and storms change diving conditions fast:

• Runoff. Rain washes sediment and bacteria into the ocean. San Diego County advises avoiding ocean contact for 72 hours after rain, especially near river mouths, storm drains, and lagoon outlets.
• Swell. Bigger, more frequent storm swells stir up the bottom and bring surge to shallow reefs.
• Extreme tides. Scripps expects very high tides around November 24, December 24, January 22, and February 19. Strong tidal flow can stir up sediment and change current direction at canyon and bay-mouth sites.

More from the blog: Best time to dive La Jolla Cove · San Diego spearfishing spots and conditions · The "Do Not Eat" fish advisory explained