Though the situation appears to be improving, the upper reservoir remains closed at Veterans Memorial Lake Park.
Norwalk officials placed the upper reservoir under a recreational advisory Monday after a bloom of blue-green algae was discovered in the northwest corner and western edge.
The advisory means humans and pets should steer clear of the upper reservoir while the water is being treated. The blue-green algae releases potentially harmful toxins into the water.
The city's drinking water supply, which comes from the lower reservoir, is unaffected, said Josh Snyder, public works director.
Water samples are being sent daily to a testing facility on Gibraltar Island on Lake Erie.
"The tests are still exceeding acceptable limits," Snyder said.
The city treated the upper reservoir with 750 pounds of copper sulfate Monday.
Water department personnel was treating the upper reservoir with liquid copper Wednesday.
"We're giving it a second dose, though there have been visible improvements," Snyder said. "We don't have the green sheet like we did Monday. We're just waiting for the chemistry to catch up with what we're seeing."
Snyder said the city isn't treating the memorial reservoir.
"But, we are testing all three reservoirs at the same time and from different locations," he said.
Snyder said taking water from Northern Ohio Rural Water is always an option, if, in a worst-case scenario, all three reservoirs would develop a problem with blue-green algae.
"I'm sure rural water would like to sell us a lot more than we've been buying," Snyder said.
Snyder described the treatment process at the upper reservoir.
"We take the granular products and tow it behind a boat in a burlap bag," he said, adding when the water comes across the bag, the chemical is released into the water.