The spillway gates lift upward, allowing the water from the bottom to flow from the lake, not from the surface where the salvinia grows.
Lowering the lake in this manner leaves salvinia floating on top and not flowing over the spillway. It creates isolated pockets of the stuff that now cannot be reached to spray. It leaves the salvinia that was trapped in the cypress breaks, still trapped in the cypress breaks. The salvinia that gets stranded along the exposed lake banks does not die it just lays there until the water level returns.
There are those of us who believe that creating a current in the lake is the correct approach, but not from the bottom of the lake. The current has to be created at the surface level in order to carry the salvinia over the spillway. To do this, the lake has to be brought up above its normal level and then allowed to flow over the spillway.
This is a cheap, easy, and we believe an effective way to control the growth.Simply sand-bag the spillway bringing the lake level up 2-ft. Then remove the sand-bags allowing the water to flow over the spillway carrying the salvinia away. This should be a continous process throughout the year.
Raising the water level would also enhance the flow of the salvinia from the trapped cypress breaks. A cypress tree's trunk is much smaller above the water line. By forcing the large root base below the water's surface, you have now created more space between the cypress trees that would allow more of the salvinia to flow freely with the wind and current.
A simple and we believe an effective approach to controlling this plant. The truth is that the salvinia in Lake Bistineau will never be eradicated, but it can be controlled in this cost effective manner.