Is Lake Tapps safe to swim in?

The short check before you jump in

It takes about as long as finding a towel.

• Look up the current surface water advisories on the Tacoma-Pierce County Health Department website. Lake Tapps is one of the lakes it tracks.
• Read any sign posted at the park, the community beach or the launch. Signs go up where an advisory applies, and the wording on the sign tells you what to avoid.
• Look at the water where you plan to get in. Scum, streaks of bright green or blue-green, or water that looks like pea soup or spilled paint are reasons to stay out, advisory or not.
• Keep dogs out of any water you wouldn’t go into yourself.

Most of the time, that check ends with a swim. The point of doing it every time is that conditions can change quickly, and the lake at your dock isn’t always the lake across the way.

What blue-green algae is and why it blooms

The “toxic algae” in the headlines is cyanobacteria, often called blue-green algae. It lives naturally in lakes all over Washington, Lake Tapps included, and most of the time it stays in the background.

A bloom happens when conditions let it multiply fast. The usual recipe is warm water, long sunny days, calm weather and a supply of nutrients, mainly phosphorus and nitrogen. Those nutrients reach a lake from lawn fertilizer, failing septic systems, pet and goose waste, and soil and leaves that wash in with rain. In western Washington lakes, blooms tend to show up in late summer and early fall, when the water has had months to warm.

Two details catch people out. First, some blooms produce toxins and some don’t, and you can’t tell which by looking. That is why the health department relies on lab testing, and why the safe habit is to treat any visible bloom as a problem until someone says otherwise. Second, wind moves a bloom around. Scum drifts to the downwind shore and piles up in coves and against docks and bulkheads, so one side of the lake can look fine while a sheltered corner on the other side is thick with it. A calm, hot week can concentrate it in exactly the shallow spots where kids and dogs like to wade.

Who tests the water and how advisories work

The Tacoma-Pierce County Health Department is the agency to watch. It monitors lakes around the county, including Lake Tapps, sends samples to a lab when a bloom is reported or seen, and posts advisories on its website with the affected lake or area. It also takes reports from the public, so if you see what looks like a bloom, you can report it.

Cascade Water Alliance, which owns and manages the reservoir, also keeps an eye on water quality and shares lake information on its website. For anything about the current lake level, Cascade is the source. For whether it is safe to swim today, go to the health department.

Advisories in Washington use tiered signs, running from Caution up through Warning and Danger. The lowest level generally means a bloom is present and you should avoid the scum and keep pets out. The higher levels mean toxins have been found at levels that call for staying out of the water, and the highest can close an area entirely. The exact advice for each level is printed on the sign and in the posting, so read the words on it before you decide. An advisory can cover part of the lake and not all of it, and it stays in place until testing shows the water has cleared.

Dogs, kids and the shallow coves

Dogs are the most at risk, and it isn’t close. They drink lake water, they wade through the scum that collects along the shore, and afterward they lick it off their fur. A dog can swallow far more than a person would in a whole afternoon of swimming.

If your dog goes into water that might have a bloom, rinse it off with clean water right away, before it starts grooming, and watch it closely. Signs of poisoning in dogs can include vomiting, drooling, weakness, stumbling and seizures, and they can come on fast. Call your veterinarian or an emergency vet immediately and tell them you suspect toxic algae.

Small children are the next concern for the same reason: they swallow water and play in the warm shallows where scum drifts. People who have had contact with a bloom can get skin irritation or a rash, and swallowing affected water can cause stomach illness and, with some toxins, more serious effects. If someone feels sick after swimming in water that looked off, call a doctor or the Washington Poison Center and mention algae.

Swimmer’s itch is a different problem

Plenty of people who get an itchy rash after a swim assume it was the algae. Often it was swimmer’s itch, which is unrelated.

Swimmer’s itch is caused by tiny parasites whose normal hosts are waterfowl and freshwater snails. The larvae mistake a swimmer for a duck, burrow into the skin, and die there, leaving small red, very itchy bumps that show up within hours or a day or two. It isn’t contagious and it usually clears up on its own, though it can be miserable for a few days. A pharmacist or doctor can suggest what helps with the itch, and anyone with a severe reaction should see a doctor.

It tends to show up in warm, shallow water near shore, where snails live. A few habits help: get in off the end of the dock where the water is deeper and skip long wades through the shallows, rinse off with clean water after a swim, and towel off briskly right away. Not feeding ducks and geese around your dock helps too, for this and for the nutrient problem above.

What shoreline owners can do

Nobody on the lake can prevent blooms alone. But the nutrients that feed them come in large part from the land around the water, which means the people who own that land have real influence. The useful steps are ordinary ones.

• Keep the septic system healthy. Have it inspected and pumped on the schedule the health department recommends, and fix problems promptly. A failing drainfield close to the lake sends nutrients straight toward it.
• Go easy on fertilizer. Use little or none near the water, choose phosphorus-free products, and never fertilize right before rain.
• Keep yard waste out of the lake. Grass clippings, leaves and blown debris all carry nutrients.
• Let a strip of native plants grow along the shore. A planted buffer slows runoff and filters it before it reaches the water, and it tends to make a lawn less inviting to geese. Check with the city or county before doing work at the shoreline, since permits can apply.
• Pick up after pets and don’t feed waterfowl.
• Send roof and driveway water somewhere it can soak into the ground before it reaches the bank.

The health department’s septic program is the place to start on the first item, and Cascade Water Alliance can tell you what it asks of shoreline owners. For buyers, the septic item deserves the most attention. On a waterfront purchase, ask for the septic records and a recent inspection early, and see the buying on the water page for the other shoreline checks. For where to swim and paddle around the lake, the Lake Life page covers the public parks, and if a boat is part of your summer, the Lake Tapps boating rules are worth a read before the season starts.