With the cause of a fish kill still a mystery and more dead fish appearing every day, city officials Monday afternoon closed Mary’s Lake to fishing until further notice.

Lawrence Parks and Recreation officials said dead fish first were noticed late last week in the lake in southeast Lawrence.

Dead fish float along the banks of Mary's Lake. The Lawrence Parks and Recreation Department announced the closing of Mary's Lake to fishing on Monday because of the unexplained die-off of the fish.

But testing Monday afternoon by the state departments of Health and Environment and Wildlife and Parks failed to find the primary cause of the fish kill.

The lake’s oxygen levels were found to be lower than desirable, however, due to an algae bloom.

Fish kills can occur during periods of abundant growth of vegetation or algae.

“Parks and Recreation Department staff is exploring the addition of an aeration system to the lake, which can help add oxygen to the water,” the city said in a news release.

Additional testing may be done if aeration is not successful in halting the kill.

The department will keep the five-acre lake closed at least throughout the week.

The lake is located in Prairie Park, 2811 Kensington Road. It is stocked with a variety of fish by the Kansas Department of Wildlife and Parks.