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a field with a sign in the foreground and a mountain in the background.
Blanca Peak (Sisnaajini, or White Shell Mountain) is the backdrop for many state and federal waterways and refuges near Monte Vista, where anglers and birders flock. Photo taken July 15, 2022. (John McEvoy, Special to The Colorado Sun)

Colorado state wildlife officials are investigating whether an errant crop-duster is to blame for toxic agriculture herbicides poisoning Home Lake State Wildlife Area near Monte Vista in southern Colorado, killing snails that fish eat and forcing closure of the lake to anglers. 

The toxic “swath” appears to be a mile wide, state officials said in a release. 

The state has halted fishing in Home Lake for at least two weeks and will continue testing to find the extent of the damage, said southwest area wildlife spokesperson John Livingston. No fish die-offs have been recorded, but anglers should not eat anything they caught from the lake before the closure. The state announcement was first noted in the Alamosa Citizen.  

Home Lake State Wildlife Area is bounded by other state wildlife land as well as private agricultural plots, and investigators are interviewing crop-dusting operations in the area, Livingston said. Once investigators determine how the herbicides arrived at the site, the state could decide whether any civil or criminal action could be taken, Livingston added. There have not been many similar incidents in recent Colorado Parks and Wildlife history. 

“We are aware that there was a crop-duster working some fields in that area late last week,” Livingston said. The water was tested Friday. “Home Lake not only shares a boundary with two of our other state wildlife areas, but also some agricultural fields, and also a solar array. With the way the winds traditionally kind of move in that area, southwest to northeast direction, certainly those agricultural fields there seem likely. It’s something we’re looking strongly into right now.”

State wildlife officers are working with the Colorado Department of Agriculture on the inquiry, he said. The state does not use the herbicides.

“One of the chemicals is known to have significant impacts in invertebrates, and obviously with fish eating those, we are waiting to see what develops there,” Livingston said. “We’re also checking to just see how concentrated the chemicals are in the water. If they got pretty diluted relatively quickly, that can change the official response to this.” 

One of the detected chemicals is Flumioxazin, Livingston said in forwarding the test results. “It is practically non-toxic to bees and avian species. It is slightly to moderately toxic to freshwater fish and moderately to highly toxic to aquatic invertebrates,” he wrote, in an email. 

“The second one has two active ingredients, S-Metolachlor and Metribuzin. This is the one that takes longer to break down and has led to the fishing closure. It is described as not persistent in soil. Stable in water. Moderate mobility in soil. Sinks in water (after 24 hours),” he said.

The wildlife area is about a mile and a half east of Monte Vista, and the lake hosts rainbow trout, channel catfish, largemouth bass, bluegill and carp, the state said. There are not large deer or elk herds in the area, which is bordered by some of the famous San Luis Valley potato fields. But there are waterfowl in the lake, and it’s impossible to keep them away from the affected area, Livingston said.


“As part of the investigation, we will continue to monitor how far this does extend,” parks and wildlife area manager Rick Basagoitia said. The poisoning does not appear to have hit the bordering Shriver & Wright or Rio Grande State Wildlife Areas. Wildlife lakes and marshes in the area are popular as well for the sandhill crane migration and other birding. 

The Home Lake closure will last at least two weeks, state officials said. 

Michael Booth is The Sun’s environment writer, and co-author of The Sun’s weekly climate and health newsletter The Temperature. He and John Ingold host the weekly Sun-Up podcast on The Temperature topics every Thursday. He is co-author with...