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State and federal wildlife officials are reporting a "moderate" case of an annual avian botulism outbreak on the marshes of the Great Salt Lake resulting in the deaths of tens of thousands of waterfowl and shorebirds.
"My best guess for the entire summer along the Great Salt Lake marshes is that it has taken 25,000 to 50,000 birds," said Tom Aldrich, migratory bird coordinator for the Utah Division of Wildlife Resources. "That's what I would categorize as a moderate year."
Avian botulism is a naturally occurring toxin in marshes, activated by warm temperatures and a lack of oxygen in the water. Outbreaks generally happen every August along the Great Salt Lake marshes.
"We have studied it for 60 years and we still can't predict when we will have a bad year," Aldrich said. "In the late 1990s, we had a year where we lost half a million and some years it only impacts a few thousand birds."
Records on outbreaks date back to the 1800s and officials reported "millions of lost birds" each year, according to Aldrich.
This year's round of botulism was first noticed in late August at the state-owner Farmington Bay Waterfowl Management Area. U.S. Fish and Wildlife Service officials at the Bear River Migratory Bird Refuge west of Brigham City are now reporting dead birds.
Young hunters participating in the special youth waterfowl hunt day Sept. 19 on marshes around the Great Salt Lake will notice dead and dying birds. The birds will also likely still be visible when the general waterfowl season opens in Utah on Oct. 3.
Leslie McFarlane, wildlife disease coordinator for Utah, said the annual outbreak is specific to birds and the "chance of it affecting people is very, very small."
In recent years, however, there have been reports of dogs used to retrieve downed ducks for hunters being paralyzed from the toxins.
"The dead birds were basically being used to train the dogs," McFarlane said. "They were exposed to a huge amount of the toxin. The dogs recovered, but it took a good deal of doctoring to get them better."
McFarlane said the Harold Crane and Ogden Bay waterfowl management areas west of Ogden seem to be the hardest hit this year. Managers of those areas are increasing water flows to try and help reduce the level of botulism toxins.
The outbreaks typically end with cooler weather and rain.