Six people in a boat floating in the water.
People floating on river boat
It is said that the boat is floating on water in the first sentence, no reference to what sort of body of water, such as a "river", that the boat flows in.
exists e1 x1 x2 x3 x4.(n_water(x4) & a_topic(x1) & in(x1,x2) & in(e1,x4) & Actor(e1,x3) & v_float(e1) & (x2 = x3) & n_boat(x2) & n_people(x1) & card_eq_6(x1))
exists e1 x1 x2 x3 x4.(a_topic(x1) & on(e1,x3) & n_boat(x3) & of(x3,x4) & n_river(x4) & Actor(e1,x2) & v_float(e1) & (x1 = x2) & n_people(x1))