AUSTIN (KXAN) — With rain in the forecast over the next two days, scientists are watching closely to see what kind of impact the weather will have on toxic algae blooms that popped up in Austin waterways earlier this summer.

Several dogs died after swimming in Lady Bird Lake and near Red Bud Isle. Analysts suspect toxins produced by blue-green algae blooms may be the cause.

The city closed Red Bud Isle and has been warning dog owners not to let their pets swim in the lake since early August. City scientists with the Watershed Protection Department are collecting water samples to test for toxins every week, said Brent Bellinger, an environmental scientist with the department.

• Algae in Lady Bird Lake possible cause of death for at least two dogs

Bellinger collected the most recent sample on Monday. He’s seeing less algae on top of the water lately, and toxins are tied to the amount of algae alive to produce them. While there might be lower levels of toxins, the department is still finding positive tests and the water is not safe for pets.

Rain could have both positive and negative impacts on algae growth, thus on toxin levels, said John Higley, CEO of Austin-based research company EQO.

On the positive side, more water flow and cooler water temperatures are bad for algae, and with the most widespread rain chances the area has seen in 10 weeks coming this week, rain would likely improve both of those elements.

In the short-term, it could mean a decrease in the number and size of algae blooms in the water.

In the longer-term, though, the negative can start to outweigh any immediate benefits.

“Nutrient loading is something that we’re concerned about and runoff can actually feed the bloom,” Higley said.

As water flows through the landscape, it picks up nitrogen and phosphorous from fertilizer and other sources. Those nutrients feed algae, causing more and bigger blooms to form.

The rain will cool the water, but likely not enough. The city’s last measurement put the temperature in Lady Bird Lake at 80 degrees, Bellinger said. The temperature, Higley added, that blue-green algae begins to out-compete native algae.

It starts growing around 74 degrees, he went on, so waterways would need extended periods of water temperature below that in order to significantly impact the algae’s ability to survive.

“You can’t just tell by looking at it,” Higley said. “With this rain, it certainly will churn that up, so the water might look a little bit nicer, but that doesn’t mean that the toxin level is safe.”

In other words, don’t expect to take your dogs swimming this weekend, even if you don’t see any more algae.

The city doesn’t intend to change its advice to dog owners to stay out of the water due to the rain. Red Bud Isle remains closed, and signs warn pet owners not to let their animals swim or drink from Lady Bird Lake.

Bellinger said they’ll keep a close watch on the water in the coming days and might collect additional samples later this week if they see any changes due to the weather.

But it will still likely be October — at the earliest — before the city will be able to deem the waters safe for dogs again.

“We have to see a clean bill of health for a few days before I would feel comfortable getting back in there personally,” Higley said.

He added this probably won’t be the last team Austinites have to deal with toxic algae blooms. His research has helped draw a connection to zebra mussel infestations and blue-green algae; the invasive species eats good algae, reducing competition for the neurotoxin-producing blue-green type.

“We’re going to see this again and again,” he said. “As long as there’s zebra mussels in those lakes and we continue to have warm summers, we’re going to see this problem.”