Records and interviews show that Tempe officials knew encephalitis-carrying mosquitoes were breeding in huge numbers west of the downstream dam as far back as July. They knew the insects were proliferating to a lesser extent east of Town Lake's upstream dam, but elected to keep the information quiet.
Not only did Tempe fail to inform residents near the lake of the potential health hazard, the city did not directly alert residents to more than a dozen pesticide applications -- including malathion and a closely related chemical agent -- by a fogging apparatus leading up to the November 6 public opening of the lake.
Rather than publicly acknowledging the mosquito outbreak, Tempe officials -- including Mayor Neil Giuliano -- spoke of a breeding frenzy of midge flies near Town Lake. While nuisances, midge flies do not pose a public health threat.
Mosquitoes, however, can carry encephalitis, a disease that can cause death in children and the elderly.
Giuliano says he didn't know about the mosquito infestation downstream from Town Lake.
"Is there one?" he asked New Times.
Maricopa County health officials were well aware of the problem, as were several department heads in Tempe, including city engineer Howard Hargis and water management division manager Don Hawkes.
County environmental services director Al Brown says his staff worked overtime, weekends and nights to successfully abate mosquito infestations not only in the Salt River bed but in several other areas of the county.
"We made an extraordinary effort to go out there and get bugs," Brown says.
Brown said the county stepped up eradication efforts after mosquitoes were found to be carrying encephalitis -- particularly mosquitoes in the Salt River bed.
"It's the first time we have found Western equine encephalitis in the mosquito population in that area," Brown says.
Seven people contracted encephalitis in Arizona this year, including five in Maricopa County. Two cases were fatal. An 8-year-old Queen Creek girl who had suffered mosquito bites died of encephalitis on September 23. The second fatality is believed to be a Scottsdale man.
Craig Levy, who manages the state Department of Health Services' vector-borne and zoonotic disease section, wouldn't say on Monday whether laboratory tests have eliminated mosquitoes as the transmitter of the disease in the two fatalities. He provided general information about five of the encephalitis cases for which testing has been done. Mosquitoes have been definitively ruled out as the source in only one case, Levy says.
Tempe City Manager Gary Brown says it is not the city's responsibility to notify Tempe residents of the encephalitis-carrying mosquitoes -- or of the subsequent treatments. Brown says the city left notification to the discretion of the state health department.
"I have enough faith in the health department that if they felt there was a health risk, they would have notified people," Brown says.
The state health department did issue a September 1 press release warning of increased numbers of mosquitoes carrying the encephalitis virus in Chandler, Gilbert, southwest Phoenix and Tempe. The press release stated that mosquitoes carrying encephalitis are found almost every year in Arizona. The release stated that during the summer there was "significant increase" in the number of mosquitoes carrying the virus.
The release, however, did not identify any specific mosquito-breeding hot spots such as the areas east and west of Town Lake. Levy says the state did not identify specific breeding areas because officials wanted the public to take precautions regardless of where they lived.
Tempe community relations manager Nachie Marquez says the state never told the city that it should alert residents near the Salt River of the extraordinary high level of mosquito breeding.
She says "at no point" was Tempe "told it was a crisis nature and that you need to get specific information to the public."
Marquez says the city was taking steps internally to address the matter. The city, she says, asked the state health department and the county Environmental Services Department to write letters describing the seriousness of the situation. Those letters, she says, were forwarded to the U.S. Army Corps of Engineers as part of a city request for permission to clear mosquito-breeding habitat west of the dam.
The county Environmental Services Department and the state health department wrote Tempe in early September, detailing the extent of the mosquito outbreak.
"The area downstream of the Tempe Town Lake dam has become a potential health hazard, due to mosquito breeding activity in the area," stated a September 3 letter from John Townsend, vector control manager for the county Environmental Services Department.