Algae isn’t scary; it can actually be good

“Definitely in 2018 was the largest amount of algae in the upper part of the river, in anybody’s memory, and we haven’t seen an increase of quite as much since,” Patterson said. “I still don’t have a full answer as why specifically 2018. People have been saying in general the amount of algae in the river is increasing over the last couple of decades. My idea on that with the timeline is caddisflies would have been having ideal conditions, when the river was fully flatlined until around 2000, and since then, we’ve been returning at least some flooding to the river, and that’s starting to remove some of the caddisflies and build up the algae again.”

Patterson said the flooding that Trinity River Restoration Program has been putting in the Trinity River for the past two decades helps knock off some of the Caddisflies eating algae off the rocks. Caddisflies are insect larvae which eat algae.

These caddisflies will eat all of the algae off of rocks, leaving only a thin invisible film of algae on the rocks, not allowing other organisms to eat the algae, according to Patterson this is why the floods that Trinity River Restoration Program bring in every May help balance things out.

“It helps remove some of the caddisflies so you can grow thicker algae for the midges, the beetle larvae, the fly larvae and the various types of larvae, which do well in thicker algae,” Patterson said, “Those are the juicy morsels for young salmon. It’s good to have areas that aren’t being mowed off by caddisflies.” Although too many caddisflies, aren’t good, Patterson wanted to make it clear, they’re not bad.

“They mow off the algae, so you don’t have a large buildup, it’s just part of the ecology. I don’t want to say they’re bad a thing,” Patterson said. “Certainly the adults landing on the water to lay eggs are good fish food, for larger fish, but they’re generally not food for small fish, because caddisflies larvae build these houses around themselves with pebbles and sticks to keep fish from eating them, but for large fish, they’re a good mouthful.”

Improving the food web wasn’t something they were looking at when flooding the river every year, they were more so trying to reform the banks to move gravel where the salmon might spawn on, but with it came what seems to be a practice which is helping create more salmon food, although Patterson said it would be better if they could flood the river a different time of year.

“Ideally the biggest peaks would be December, January, February, because that’s when it naturally would’ve been happening, that’s what the salmon evolved for. The challenge is figuring how much water we have available to do those peaks when we still have most of the year to go through,” Patterson said. “This year in December was looking great, then in January the skies just cut off, and so we got no more water and we’re in a critically dry situation.”

According to Patterson, algae help salmon thrive, bringing in more bugs for the salmon to eat, so people don’t need to be so scared of algae.

“The point I’m trying to make is, we always worry about algae. ‘Oh my god, it’s a bad thing,’ but from an ecological view, we want some algae there. I still don’t have a clear answer on exactly how much we want. But we definitely want some,” Patterson said.