Ramps on Lake Manitou to open July 1

Indiana DNR Release:

The Department of Natural Resources' boat access site on Lake Manitou, which has been closed since late April to allow for treatment of the highly invasive plant hydrilla, will open July 1. The city boat ramp on the northwest corner of the lake also will open, which is a change from last year’s procedure.

The DNR decided to open the ramps after a recent survey found no viable hydrilla plants in the lake.

Despite the findings of the survey, the threat of spreading the plant to other waters still exists. Signs remain at access sites on Manitou to remind boaters to self-inspect their watercraft, motor and trailer for signs of plants when taking them from the water. All plant material should be removed and disposed of at the ramp before the boat is towed. Mud should be rinsed from the boat and trailer before transport since hydrilla tubers could be present.

Boating equipment should dry for five days before being used in another body of water. These precautions should be performed not only at Manitou but at all waters to prevent the spread of a host of aquatic invasive species, not just hydrilla.

"Through the 2009 treatment, the hydrilla tuber population has been reduced by 95 percent, compared to pre-treatment levels," said Doug Keller, DNR aquatic invasive species coordinator.

The herbicide Sonar was initially applied on May 7. The need for future additions of herbicide will be determined through frequent testing to determine the level of Sonar in the water. A concentration of Sonar lethal to hydrilla will be maintained in the lake through Oct. 15. By this date the water temperature should have cooled enough that hydrilla tubers would no longer be expected to germinate.

“Hydrilla tubers can sprout at any time water temperature is 55 F or warmer, which requires that a concentration that is lethal to the plant be maintained throughout the growing season to eliminate newly sprouted plants,” Keller said.

Sonar, with the active ingredient Fluridone, is an aquatic herbicide produced by SePRO Corporation of Carmel. Humans, fish and other aquatic life are not harmed by Sonar, especially at the extremely low rate being used at the lake, according to Keller.

Another tuber survey will take place this fall to determine the continued attrition of the tuber bank and another plant survey will be performed mid-summer.