By Gigi Hanna

When it's a matter of keeping your drinking water safe, some people dive right into the job. Literally.

Metropolitan Water District has two teams of scuba divers who regularly plunge into the handful of lakes and miles of pipelines and canals that make up MWD's massive water supply network.dives

The six-member water quality dive team is the district's first line of defense against a proliferation of algae—the slimy green stuff that can make your tap water smell or taste funny. The group dives about once a week to ensure that the water flowing out of Metropolitan reservoirs is odorless and tasteless.

The other five-member "maintenance diving team" backs up that effort by keeping the "equipment"—including 242 miles of pipeline, 63 miles of canals and 144 underground siphons-working to deliver high quality water to the 17 million Southern Californians who rely on Metropolitan for their drinking water.

Algae, the same stuff that some health-conscious people pay extra for a shot in their fruit smoothies, is a common problem in bodies of water ranging from a dog's water dish, to fish tanks, swimming pools and lakes. In some cases, it's little more than an unsightly menace that can be scraped off or killed with a dose of chlorine. In drinking water reservoirs, however, algae can give tap water an unpleasant, musty smell and taste, detectable even in very tiny doses.

When that happens, the water quality divers start pulling on their wetsuits for a little detective work.

"You can't see algae growing on rocks from the surface; the only way to make good observations is under water," said David Crocker, dive coordinator and one of the original members of the water quality dive team, which began in 1981. "It's basically a search-and-destroy mission. We're trying to constantly update our knowledge of what's going on in the reservoirs so we don't get caught by surprise."

Forget the exotic fish and fancy kelp gardens that lure recreational divers. There's little glamour in the job, said Dennis Otsuka, one of the founding members of the water quality dive team.

"Mostly what we see is a lot of mud," he said. "When we go diving where there's good visibility is pretty darn exciting for us. It's great to actually see something instead of being in zero visibility where all you can see is the glass on your mask and then mud."

Diving for clues

There are hundreds of types of algae, but only a very few cause taste and odor problems. Most often, the culprits produce one of two chemicals—methyl isoborneal (MIB) or geosmin. Both cause earthy-musty flavor, but there are distinct differences. Geosmin is the chemical that gives beets their flavor. And MIB creates the odor of freshly turned earth. Neither is dangerous to humans.

"It's an aesthetics issue, not a health concern," said Crocker, who describes himself as a microbiologist first and a diver second. "But it turns out that people are extremely sensitive to the two odors."

Even in extremely low levels—five parts per trillion, equivalent to 50 drops in the Rose Bowl if it were filled with water—people can detect the flavors even after the thorough treatment process at MWD.

There are two ways Metropolitan's water quality lab knows there's a problem with algae. One clue is when phone calls start pouring in, with complaints about the taste of the water. The lab also gets weekly and monthly samples from the treatment plants and reservoirs, respectively. In the summer, when alga growth is greater, lakes get sampled every other week. If the lab analyses show the level of MIB or geosmin rising in a particular lake, the team sends divers out to look for the algae that are causing the problem and bring back a lot more samples—some for the lab and, for a panel of trained taste-testers.

"We try to catch it before it gets to the point where the water is not acceptable," Crocker said. "When we know we have a problem and cannot find it, we take a taste-tester on the boat, a diver goes down to get a sample and bring it up, but it's real rare."

Even though he volunteered—begged even—for the assignment, Otsuka said that, after 20 years of diving into cold, sometimes algae-ridden water is still kind of disgusting.

"We're always sniffing things that are floating in the water," he said. "If we see algae floating in the water, we squish it between our finger (to determine the type)."

Sometimes, the problem is a little harder to find.

In the late 1980s, the water quality tests were showing levels of MIB in Lake Mathews, in Riverside, but the divers couldn't find the source of it. Dive after dive proved fruitless.

Then, they dove twice as far as normal, down 80 feet, and found the culprit—an underwater field of dark purple algae called phormidium.

"We had never found any problem algae below 30 feet deep," Crocker said. "At that time a new-to-us algae that grew from 40 to 80 feet deep in the winter began causing us a great deal of problems until we finally found it.

"For two years, we were hitting our heads against the walls, being ineffective because we were looking for what we had seen in the past. We learned that you can't count on what's gone on in the past, you have to stay flexible."

There has also been a shift over the years in the type of algae that's found in the reservoirs from the kind that clings to rocks and equipment underwater to the kind that floats. Scientists don't know why.

"All you can say is that conditions are variable in the reservoirs so what happens in them varies," Crocker said.

Once an alga is found lurking in the water, there are several ways to deal with it.

Water system operators can use selective-withdrawal by changing the depth of an intake pipe to draw water at different depths to avoid the algae altogether. Or they can switch to a different source or blend the water with other water that has no taste, until the odor is at an undetectable level in the water.

When they decide to attack the algae, there are two weapons—copper sulfate or chlorine.

Copper sulfate is murderous to algae, but relatively harmless to fish, birds and humans. The chemical is a deep blue crystal that can be dropped into large reservoirs via helicopter. After 48 hours, divers go down to assess the effectiveness of the treatment, and to collect new samples of water and algae.

If they can pinpoint the offending bloom, they can treat only the area where it is growing.

Chlorine, which would be prohibitively expensive and environmentally impossible to use in larger reservoirs, keeps the shallow MWD reservoirs at Etiwanda and the forebay at Diamond Valley Lake, near Hemet, algae-free.

"The algae you find in those reservoirs usually won't cause taste and odor problems, they are more likely to cause clogging problems in outlet structures," Crocker said. "Because the reservoirs are smaller—10-15 feet deep—we can go in and dump a tanker of chlorine in to take care of the algae.

"We could never chlorinate Lake Mathews because there's fish and game and it would be too toxic. And we'd never be able to put enough in (to kill the algae)," he said.

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