He then plunged bravely into the bloody waters, swam about seeking for the monster's retreat, and dived deep.

At last, descrying a phosphorescent gleam in the depths, he quickly made his way thither, shrewdly conjecturing that it must be Grendel's hiding place.

But on his way thither he was repeatedly obliged to have recourse to his sword to defend himself against the clutches of countless hideous sea monsters which came rushing toward him on all sides.
"While thro' crystal gulfs were gleaming Ocean depths, with wonders teeming; Shapes of terror, huge, unsightly, Loom'd thro' vaulted roof translucent." J.C.JONES, _Valhalla_.
A strong current seized Beowulf, and swept him irresistibly along into the slimy retreat of Grendel's mother.

She clutched him fast, wrestled with him, deprived him of his sword, flung him down, and finally tried to pierce his armor with her trenchant knife.

Fortunately, however, the hero's armor was weapon-proof, and his muscles were so strong that before she could do him any harm he had freed himself from her grasp.