Gee, do you think you could take some time to explain exactly what it is your trying to do.
Read your own post, are you going to back the truck up and just fill the lake with concrete? Of course not but we have no way to know.
Perhaps this is an effort to defeat the invading asian shrimp by filling their habitat with concrete. Or maybe induce the burmese pythons to move to a new location? Or perhaps the OPS has a serious project in mind?
Seriously, there are many ways to form and place concrete underwater, the appropriate technique depends on a careful, precise description of exactly what it is you need to accomplish, and any constraints you are under.