a man is wakeboarding in a lake
the man is at the lake
To do stuff in a lake (such as wakeboarding in it), one generally has to be at the lake in question.
exists e1 x1 x2.(in(e1,x2) & n_lake(x2) & Actor(e1,x1) & v_wakeboard(e1) & n_man(x1))
exists p1 x1 x2.(n_lake(x2) & n_man(x1) & at(x1,x2))