A mass fish kill that prompted Lubbock officials to add a chemical to city water was being blamed on a toxic algae bloom - and certainly not being connected to recent reports of mass animal deaths around the country, officials said Thursday.

Between 10,000 and 20,000 gizzard shad were found dead last week in Lake Meredith, prompting Lubbock officials to continue adding a chemical to Lubbock water to prevent a possible fishy odor from reaching Hub City faucets. The fish kill triggered state officials to investigate the mass deaths.

The likely culprit: golden algae, a water-dwelling organism that, under certain conditions, can release a toxin fatal to fish, said Charlie Munger, a district supervisor for the Texas Parks & Wildlife Department.

Munger said low water levels at Lake Meredith likely increased salinity and PH levels in the dwindling lake. That chemical imbalance, along with cold temperatures, likely was enough to affect the algae's ability to survive and trigger its defense mechanism - releasing toxin to kill other organisms to provide nutrients.

The toxin damages the gills of fish but is not believed to be hazardous to humans or other animals, officials said.

Munger and Kent Satterwhite, Canadian River Municipal Water Authority general manager, said they didn't believe the deaths of the gizzard shad were at all connected to reports of mass animal deaths across the country.

The reports of dead animals include 5,000 black birds found New Year's Eve in Central Arkansas, 2 million fish in the Chesapeake Bay, 150 tons of red tilapia in Vietnam, 40,000 crabs in Britain, and various species in other places across the world, according to The Associated Press.

The black birds may have died from blunt force trauma, according to a preliminary report released Wednesday by the Wildlife Health Center in Madison, Wis., and reported by the AP. All of the deaths were still under investigation.

Though not believed harmful to humans, the Lake Meredith water is being treated in Lubbock for the aesthetic problems a golden algae bloom can cause - fishy-smelling water, Lubbock Water Utilities Director Aubrey Spear said.

To do so, the city is using powdered activated carbon, a non-toxic, flavorless and odor-removing compound added at the rate of 2 milligrams per liter of tap water, he said.

The city will continue adding the chemical for the next two to three weeks, Spear said, though he was not aware of an unusual odor coming from the water transported to Lubbock via aqueduct.

"It's just precautionary," he said. "The last thing we want is people calling in saying, 'I smell something in my water.' "

The Canadian River Municipal Water Authority's increasing reliance on groundwater instead of Lake Meredith water lessened Lubbock's fishy-water threat, Spear said.

About 80 percent of Lubbock's water recently has come from wells in Roberts County.

That ratio of well water is expected to increase closer to 100 percent through May, Spear said.

Lake Meredith, a major source of water for Lubbock, Amarillo and other Panhandle-South Plains communities, in recent years has seen some of its lowest water levels on record.

The lake on Thursday was measured at the record-low level of 38.31 feet - more than 60 feet bellow its record 101.85 feet set in April 1973, according to the Canadian River Municipal Water Authority.