Austin Answered: Are those algae blooms bad for your health?

Aug 13, 2017
A view of the Colorado River in 2013 in Bastrop, between Loop 150 and Texas 71. While algae blooms in Austin waterways present no danger to human health, according to Austin officials, they have been growing in intensity in recent years. RICARDO B. BRAZZIELL/AMERICAN- STATESMAN

Over her two-plus decades in Austin, Leslie Gompf has come to accept that every year or so, the drinking water “tastes too yucky for me to drink it.”

She knows about the algae blooms that cause the taste. But lately she had several recent conversations that left her wondering if the algae emit toxins — and if anyone is monitoring the toxins. She has also wondered if they are fed by natural runoff or if there is any particular type of dumping that causes them. So she asked the American-Statesman.

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The short answer is that, yes, some of the algae emit toxins; no, they do not pose a threat to people; and the city of Austin and the Lower Colorado River Authority monitor toxicity levels to make sure the water is safe, both for swimming and drinking. Also worth noting up front: The occasional bad taste that occasionally comes through in Austin’s drinking water is not toxic.

Before we go any further, a little background:

Different types of algae and “cyanobacteria” — which are not technically bacteria, but which tend to get lumped in with them — live naturally in the Highland Lakes, which include regional water-supply lakes Buchanan and Travis. Sometimes people see algae blooms, particularly in summer. The algae blooms are different from what’s termed “aquatic vegetation,” such as hydrilla, an invasive plant the city occasionally clears out of Lake Austin.

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The algae blooms tend to be red, green or blue-green. The blooms bloom to their bloomiest when two things happen: A warm winter gives way to a hot summer, and the region slips into drought, leaving little water flowing through the Highland Lakes.

This has been a weirdly warm year, but the lakes are still about 90 percent full. Plenty of water is flowing through the lakes, which has meant relatively few blooms so far, according to the city and the LCRA. But the blooms occasionally multiply to the point that lakeside residents make calls about them.

The blooms can cause Austin’s drinking water to have what Austin Water Utility spokeswoman Jill Mayfield called “a more earthy and grassy taste and smell.” When that happens, the utility treats the water until it returns to its normal taste and smell, Mayfield said. The city has a North Austin chemist who tests and tastes the water each day, she said.

It can affect the taste and smell of it, but it does not affect the quality” or make people sick, Mayfield said.

However, there is a certain kind of algae bloom — the cyanobacteria, the stuff that isn’t technically algae — that city officials keep a close eye on. Cyanobacteria is the type of bloom that most people notice, on account of its color (blue-green), its proclivity to stay as near to the surface as possible and its likelihood of appearing in late summer “when everyone is out on the water,” said Brent Bellinger, an ecologist with the city.

Cyanobacteria does produce toxins. This is what Gompf heard, and what concerns her.

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“I have friends who are multiply chemically sensitive, and they have talked about how they can react quite badly to cyanotoxins,” she said, adding that some types of cyanotoxins are not regulated by the government.

Bellinger said that “a suite of conditions related to nutrient chemistry, grazing organisms, competition … have been implicated in stimulating toxin production.” But the city monitors cyanotoxins and has not found them to occur in the Highland Lakes at levels harmful to people, he said.

He said the cyanobacteria tend to grow naturally and that no single point, such as large-scale dumping, appears to be responsible for them. In Lake Austin, the bacteria are fed by nutrients from “septic systems, pipes, and roads as well … but the magnitude of their role in bloom dynamics remains to be determined.”

He also addressed a common theory that the algae (and cyanobacteria) rob the water of oxygen fish need.

They do not deprive the fish of oxygen, Bellinger said. They actually add oxygen to the water and ever so slightly enhance the risk of fish kill only when they die off and can pump less oxygen into the water. Even that phenomenon rarely kills Highland Lakes fish, though; Bellinger said they just move to an area with enough oxygen.