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Toxic Outbreak Unlikely In Valley Water Supply

(Photo by Andrew Bernier - KJZZ)
The Salt River flows under Central Avenue.

Earlier this month, a toxic algal outbreak in Lake Erie crippled the city of Toledo, Ohio, leaving residents without water access for three days. 

What happened in Toledo was a mix of increased rains, unabsorbed fertilizer from agricultural run-off and warmer than average temperatures, causing a large bloom of algae in Lake Erie. That led to the toxic algal outbreak that shut down Toledo’s water system.

Fortunately for the Valley, the chance of an algae bloom to this scale is remote. Paul Westerhoff, Senior Sustainability Scientist and Professor of Engineering at ASU explains.

“In Arizona, compared to Ohio, our Salt River and Verde River watershed have a lot less agricultural activity, in fact close to zero," Westerhoff said. "I mean, there is really very low upstream of the reservoirs. So, we don’t have as much of the fertilizer applications.”

Naturally occurring in free-floating algae is cyanobacteria, a photosynthetic bacteria that makes its energy through photosynthesis. It also produces microcystins, a toxic substance formed inside the algae cells. Those cells rupture and the microcystins are released into the water. Although this is natural, the larger the bloom, the more toxins released. Lake Erie has seen more of these occurrences as of late.

However, the Valley has seen instances where algal blooms in the water system. In the early 2000s, some very wet spring seasons and forest fires led to increased run-off and nutrients, leading to blooms and fish kills in Lake Roosevelt. Those fish kills were caused by the cyanobacteria in the algae they ate, which acts as a neurotoxin, or poison to the brain. As a result, Phoenix and ASU partnered to research if microcystins posed a threat.

“What we found are very, very low levels of these toxins in the water," Westerhoff said. "In some of these cyanobacteria, there are these microcystins, the similar toxins, but they tend not to get into the water.”

Beyond the Salt and Verde River watersheds, the other major valley water source is Colorado River water, delivered through the Central Arizona Project. Troy Hayes, assistant water services director for the city of Phoenix, explains how this water is even less of a concern.

“CAP water is cleaner, mostly because of the length of time that it takes to travel to here," Hayes said. "And a lot of that constituent has fallen out in the canal.”

Residents and commercial entities in the Valley should also be aware of the application of fertilizer on their land, such as lawns and gardens. Even the remaining farms in the Valley know of the limitations. John Scott is the owner of One Windmill Farm based in Queen Creek.

“You’re not allowed to have more run-off off your farm," said Scott. "You cannot put more water on than your farm can handle. You know it can’t run-off into the, well, you know we do have streams and creeks and stuff like that, but you can’t discharge your irrigation water into those sources”

Scott also points out one of the main reasons why many farmers, either in the upper Midwest or here in the Valley, are on the defensive about being blamed for agricultural run-off.

“Fertilizer is so expensive now that you’re not going to put on any more than you absolutely have to,” Scott said.

Although water applied to grounds doesn’t carry into the drinking supply, it does wash into the watershed, getting into upper ground water in the West Valley. Hayes explains how West Valley communities avoid this.

“So a lot of what you see in the upper aquifers is you see high nitrates, all the things you see from agriculture over the years that have been here," Hayes said. "And so most of the cities have been focusing on drilling wells lower to get into the more pristine aquifers.”

While Toldeo’s drinking water comes from where their watershed ends, the Valley’s water comes from upstream, where agricultural nutrients are minimal. And though there is no real chance of microcystins coming out of your tap, know that what you put down the drain, and onto your lawn, has to go somewhere.

Andrew Bernier was a senior field correspondent at KJZZ from 2014 to 2016.