SPARKS, Nev. (AP) -- Most locals reacted like Rick Dinoso when he first heard that all the fish in the Sparks Marina were dead -- an estimated 100,000 trout, bass and catfish.
"All the fish don't just die," said Dinoso, 37, an assistant manager at a nearby tavern who grew up in Sparks.
"That's a lot of fish," Wayne Weaver said Friday as he walked the 2-mile loop trail around the 77-acre, man-made lake with wife, Dee. "That's a lot of recreation lost."
Scientists say the massive fish kill was caused by a dramatic drop in the water's oxygen content, which they say is not all that uncommon. They believe it was triggered by a weeklong cold spurt in December when lows hovered near zero at the former gravel pit converted into a marina 15 years ago along Interstate 80 just east of Reno.
Though testing is incomplete, state wildlife and environmental officials are convinced there's no danger to humans or animals. There's been no sign of any contamination like the pollutants that leaked into the pit in the 1980s from a petroleum tank farm across the highway, they say.
Despite those assurances, city officials have been forced to respond to concerned citizens. Most worry whether it's safe to let their dogs in the water.
"It's not good for the fish obviously, but the water quality itself is great and there's no health or safety issue," city spokesman Adam Mayberry said. "Other than fishing, there's no indication you can't do anything else out there that you have always been doing."
Sudeep Chandra, a limnologist at the University of Nevada, Reno known for his research at Lake Tahoe, agrees.
"I really don't think it is other contaminants, it's just the low oxygen," he said. He said it likely occurred when the oxygen-rich warmer waters on the lake's surface quickly cooled, sinking to the bottom of the lake and causing a violent "turnover" of the waters.
A hot, dry summer may have contributed by spurring growth of oxygen-sucking algae, he said.
Wildlife officials estimate replacing the fishery will cost tens of thousands of dollars. City officials believe the economic impact is limited to the 1,800 anglers who fish there. The past five years, they've accounted for roughly 1-of-30 overall visitor user days, which totaled about 340,000 last year.
Of bigger concern is the national media coverage of the massive fish kill -- not the sort of thing the neighbors of "The Biggest Little City in the World" had in mind when they recently adopted a new city slogan, "It's Happening Here."
"Negative publicity is always a concern," Mayberry said. "Dead fish and fish floating to the bottom of the lake -- those aren't very good images."
Founded along the Union Pacific Railroad in 1905, Sparks touts the marina on its web site as a "Brownfield Success Story."
A family ranch dating to the 1860s operated on the property until it was sold in 1967 to Helms Construction Co., which dug aggregate from the pit for 25 years. Contaminants discovered in 1988 quickly were linked to the tank farm, the target since of a state-led cleanup project. The early effort included pumping out polluted groundwater that had collected in the pit.
Because groundwater constantly flows into the marina, city officials pump more than 2 million gallons a day into the neighboring Truckee River. That water has never exceeded environmental standards, including in the most recent testing in December, regulators said.
"There is no data to indicate that the (tank farm) is involved, connected or related to the dead fish," Nevada Division of Environmental Protection spokeswoman JoAnn Kittrell said.
That hasn't stopped Kristine Rowland from wondering what killed the fish. She remembers the quarry was used as a dump when she was growing up 30 years ago.
"In the old days you would just back up the truck and dump it all out," said Rowland, a Reno businesswoman. "It was like family day, and you could ride home in the back of the truck."
Wildlife officials typically restock the marina by March 1. They had planned to add 26,000 trout and 4,000 catfish this year, but won't unless the oxygen recovers.
The loss of Nevada's biggest "urban fishery" would be more significant than usual during this drought year, when low water is expected to preclude fishing at many popular reservoirs and rivers, Department of Wildlife spokesman Chris Healy said. It also would force cancellation of a youth fishing day, which annually attracts 3,000-4,000 in June.
Gary Yuill said the unfortunate collapse of the fishery won't curtail his daily dog walks.
"I don't think there's anything wrong with the water, but I understand people questioning it," he said. "It doesn't make sense."
Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.