Read the label on your bag of lawn fertilizer and help protect your favorite lake or reservoir from those smelly, pea-green algae that shut down summer watering holes for weeks at a time.
That’s the message from water quality officials and municipal water utilities this year as the summer lawn and recreation season gears up.
Algal blooms, long common in the eastern United States, are becoming more prevalent in Colorado’s lakes and reservoirs as a 20-year mega-drought reduces water levels; more frequent days above 90 degrees increase the temperature of the water; and a growing number of homeowners are adding lawn fertilizers containing phosphorus to their lawns.
Blue-green algae produce toxins that can harm people and pets and can create odors and tastes that degrade water quality.
The problem first appeared at Aurora’s Quincy Reservoir in 2020. Since then, the city has taken the initiative to try new treatment methods, such as installing aeration devices that inject oxygen into the reservoir. ‘water. He also spent millions on other treatments such as hydrogen peroxide and alum, which kill certain types of toxin-producing algae. The alum also weighs down the phosphorus so that it sinks to the bottom of the lake and becomes locked in silt and mud.
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But the biggest problem, by far, according to Sherry Scaggiari, environmental services manager at Aurora Water, is the increasing amount of phosphorus moving from lawns to stormwater and then to streams and lakes.
“We’re trying to get people to use less phosphorus on grass. You need nitrates, but you don’t need phosphorus,” Scaggiari said.
At Barr Lake State Park, near Brighton, the issue has sparked several efforts to clean up Barr Lake 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 about 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’s half the state’s population.
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Fixing Barr and Milton is a major undertaking. Treatments such as alum work best in bodies of water, such as natural lakes, where water supplies are not released each year for irrigation. Much of the Barr-Milton system is used to irrigate farmland in the Eastern Plains as well as provide municipal drinking water. It empties and refills approximately every eight months.
“We would add alum almost continuously,” Lundt said, an expensive process that also increases the park’s carbon footprint because alum has to be mined.
Aurora, however, hopes she only needs to treat Quincy once every 10 years or so, according to Aurora Water spokesman Greg Baker. But if phosphorus levels continue to rise, it may need to be done more frequently.
Lundt has also been using a method known as bioremediation to remove some 8,700 carp, or about half of the local carp population, from Lake Barr since 2014. The invasive species is known to stir up sediment, release phosphorus into water and create a favorable situation for the growth of algae.
This month, the association plans to hold a fishing contest with a $2,000 prize for the angler who catches the most carp.
And Aurora and Barr-Milton are considering 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, according to water officials, the best, and perhaps most cost-effective, tool is to reduce the use of phosphorus-based lawn fertilizers.
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The Barr-Milton Watershed Association has been running 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 year-long campaign to educate Coloradans about water issues, also shines a light on the problem. (Water ’22 is run by Water Education Colorado, which sponsors Fresh Water News).
Lundt said some 12 states have already banned the use of phosphorus-enriched fertilizers by homeowners unless they can prove their soils lack phosphorus.
Major fertilizer manufacturers, like Scott, have phased out phosphorus completely.
“The fertilizer companies are on board; it’s just about changing the culture of how we fertilize our lawns,” Lundt said.
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