Until end of turn, target creature you control has base power and toughness 4/4 and gains flying and hexproof. (It can't be the target of spells or abilities your opponents control.)
Water Wings overwrites any previous effects that set the creature's power and/or toughness to specific values. Effects that otherwise modify its power and toughness will still apply no matter when they took effect. The same is true for +1/+1 counters.