What some area river watchers refer to as the “emerald carpet” has been creeping its way along the bed of the lower Roaring Fork River earlier than usual this summer.

While the excess algae growth has prompted some alarm for casual observers, it’s not necessarily threatening the river’s health, said Rick Lofaro, executive director for the Roaring Fork Conservancy.

In addition, the recent monsoonal rain pattern should help the situation, he said.

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To be sure the algae is not affecting the river health, though, the Basalt-based nonprofit is planning to take some water samples between Glenwood Springs and Carbondale this week.

“We have been getting a lot of calls about it, so we are planning some targeted sampling around the algae patches,” Lofaro said. “When it becomes concerning, and what we look for, is whether the water exceeds the state standard for dissolved oxygen of six parts per million.”

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Normally, the algae growth isn’t as thick until late August or September when streamflows are lower, he said.

“We had a decent year for runoff and had some pretty good scouring on the river bottom, which is what you want to sweep away the sediment,” Lofaro said.

But the river levels dropped quickly after the runoff, the water cleared faster than usual, and then the hot weather hit. That allowed the sunlight to penetrate the river depths and cause the algae growth to take off sooner than usual, he said.

The algae build-up has been thicker around Glenwood Springs, but stretches upstream to the Carbondale area, observed Craig Davis, a fishing guide at Roaring Fork Anglers in Glenwood Springs. He said the algae came in almost a chartreuse color when it first appeared in mid-July.

“It did seem a little early, and usually it’s a darker green,” he said. “It does make it a little more difficult for fishing when you keep getting moss on your hook. That can be annoying.”

But it hasn’t seemed to affect the health of the fishery, he said.

“We’re still floating that stretch, but we do try not to fish as heavy or deep so we don’t get into those snags,” Davis said.

Lofaro said the Crystal River near Carbondale had similar conditions two years ago, and he’s heard of other rivers in the region experiencing excessive algae growth this year as well.

Besides natural conditions, another contributing factor that speeds the growth of algae is the extra nutrients that get added to the rivers from agricultural and golf course runoff, as well as the many septic systems that line the Roaring Fork River in particular, Lofaro added.

“Targeting the point source is difficult, but it all adds up,” he said. “The more nutrients that get into the stream it just fuels that growth.”

The seasonal monsoonal rain patterns that have started to emerge over the last couple of weeks should help the situation, Lofaro said.

The extra water and turbidity help to loosen and break up the algae and also lower the water temperature.

“We’ve had some good rain but nothing real heavy yet, so that would help even more,” he said.