Colorado trying new tools, including phosphorus-free lawns, to combat toxic algae | News

Read the label on your lawn fertilizer bag and help save your favorite lake or reservoir from those smelly, pea-green algae blooms that shut down summer watering spots for weeks at a time.

That’s the message from water quality officials and city water utilities in Colorado this year as the summer lawn and recreation season gears up.

Algae blooms, long common in the Eastern United States, are becoming more frequent in Colorado lakes and reservoirs as a 20-year megadrought reduces water levels, 90-plus degree days occur more often, raising water temperatures and growing numbers of homeowners add phosphorus- laced lawn fertilizers to their grass.

Blue-green algae produces toxins that can harm people and pets, and can also create odors and tastes that degrade water quality.

The problem surfaced at Aurora’s Quincy Reservoir in 2020. Since then the city has taken the lead on trying new treatment methods, such as installing aeration devices that inject oxygen into the water. It has also spent millions on other treatments such as hydrogen peroxide and alum, which kill certain types of toxin-producing algae and, with alum, weigh the phosphorus down so that it falls to the bottom of the lake and becomes encased in silt and mud .

But the biggest issue by far, says Sherry Scaggiari, an environmental services manager at Aurora Water, is the increasing amount of phosphorus that finds its way from lawns into stormwater — and then into streams and lakes.

“We are trying to get people to use less phosphorus on the grass. You need nitrates, but you don’t need phosphorus,” Scaggiari said.

At Barr Lake State Park near Brighton, the problem has triggered several efforts to clean up Barr and Milton Reservoir, which are owned by a private irrigation company. Steve Lundt, a scientist who sits on the board of the Barr-Milton Watershed Association, has been monitoring the watershed for some 20 years.

“People always ask, ‘Why is there so much phosphorus in these reservoirs?’ Well, there are 2.5 million people living in the watershed. That is half the population of the state.”

Fixing Barr and Milton is a major undertaking. Treatments such as alum work best in water bodies such as natural lakes, where water supplies aren’t released annually for irrigation. Much of the Barr-Milton system is used to irrigate farm lands on the Eastern Plains as well as to supply municipal drinking water. It drains and fills every eight months, roughly.

“We would be adding the alum almost continuously,” Lundt said, an expensive process that also expands the park’s carbon footprint because the alum has to be mined.

Aurora, however, hopes it only needs to treat Quincy once every 10 years or so, according to Greg Baker, spokesperson for Aurora Water. But if phosphorus levels continue to rise, it may have to be done more frequently.

Lundt is also using a method known as bioremediation to remove some 8,700 carp — or roughly half of the local carp population — from Barr Lake since 2014. The invasive species is known for stirring up the sediment, releasing phosphorus into the water and creating a situation ripe for algae growth.

This month, the association plans to hold a fishing competition with a $2,000 prize for the angler who removes the most carp.

And Aurora and Barr-Milton are looking at extensive planting programs along waterways leading to their reservoirs that will use plants, such as cattails, that are effective at removing phosphorus from water.

Still, water officials say, the best tool — and perhaps most cost-effective — is to begin slashing the use of phosphorus-based lawn fertilizers.

The Barr-Milton Watershed Association has been leading a campaign, called the P-Free Lawn Fertilizer campaign, to encourage consumers to omit phosphorus from lawn care for several years. And Water ’22, a yearlong campaign to educate Coloradans on water issues, is also highlighting the issue (Water ’22 is being led by Water Education Colorado, which sponsors Fresh Water News).

Lundt said some 12 states have already outlawed phosphorus-enriched fertilizers’ use by homeowners unless they can prove their soils are short of phosphorus.

Major fertilizer makers, such as Scott, have removed phosphorus altogether.

“Fertilizer companies are on board; it’s a matter of just changing the culture of how we fertilize our lawns,” Lundt said.

Fresh Water News is an independent, nonpartisan news initiative of Water Education Colorado. WEco is funded by multiple donors. Our editorial policy and donor list can be viewed at

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