Stream bugs offer clues to health of Bainbridge waters

Caddisfly casings cling to a rock pulled from Bainbridge’s Cooper Creek on Wednesday. (Below) a frog keeps a wary eye on its surroundings. (Tad Sooter photos)

When fly fishermen approach a stream they watch for a few familiar bugs. A flurry of mayflies, caddisflies or stoneflies tell an experienced angler what food fish are rising for.

When water quality specialists approach a stream they look for the same insects for different reasons. To the trained eye, those water-dwelling macro invertebrates offer clues to the overall health of a creek.

I received a crash course on stream bugs Wednesday as I tagged along with volunteers from the city’s Water Quality and Flow Monitoring Program, in preparation for a story on the city’s State of the Island’s Waters report, which was released with little fanfare earlier this summer.

Five years of data gathered from all 12 Bainbridge watersheds and around the island’s shoreline went into the report. It’s the first comprehensive study of island water health the city has completed. The report confirmed that many island streams still struggle with high levels of harmful bacteria and nutrients, and low dissolved oxygen.

Cooper Creek is a happy exception. Of the 15 streams regularly monitored by the city, all but Cooper Creek are failing state standards for harmful bacteria. That makes Cooper something of a poster child for healthy island streams.

We saw signs of life everywhere as we mucked along the banks of Cooper Creek Wendesday at the head of Eagle Harbor. City Water Resources Specialist Cami Apfelbeck pointed out caddis fly casings (pictured above) dotting many rocks in the stream bed.

Caddisfly larvae construct their own homes. They use a silk secreted from a gland in their bodies to glue together pebbles into a cozy casing. They live in these casings beneath the surface of the stream until they’re ready to sprout wings and hatch.

Caddisflies like clean water and strong flows. Their presence in a stream is usually a good omen, Apfelbeck said.

“The stoneflies, the caddisflies the mayflies, you like to see those.” she said. “These conditions are almost perfect for them.”

Caddisflies aren’t the only creatures of interest. Specialists sample for dozens of macro invertebrate species. Some are tolerant to pollution, others die off quickly in contaminated streams. Some prefer pebbles, others don’t mind mud. Knowing these tendencies, their abundance or absence in a stream is an indication of water conditions.

“The healthiest streams all show rich diversity,” Apfelbeck said.

You can read my full story on island water quality later this week in the Sun. Meanwhile, the State of the Island’s Waters report is available on the city’s website for perusal.