What does Beowulf do after he defeats the water witch?

He decapitates Grendel's dead body and returns to the top of the lake.

Explanation:

Here's the part from the story, "After he killed the Water Witch, he looked by the fire and saw Grendel's body lying next to it. He cut Grendel's head off and headed back to the top of the Lake. As he reached the top everyone including me praised him and cheered to him. This was once again another time that Beowulf had saved my people from evil."