Grenade Fishing is a challenge in Hunter's Grotto that requires players to collect fish by throwing grenades into pools of water. There are three pools of water across the map, indicated by a chair and a fishing rod. When a grenade is thrown into the water near the fishing line and explodes, several fish will appear on the surface of the water. Players collect ten of these fish to complete the challenge. You can also use the Corrosive Fan Boat to get the fish out.
The first pool is in the central north area of the map, northwest of the lodge and directly south of the exit to Ardorton Station, to the west of the broken bridge leading to the map exit. This pool will yield three fish.
The second pool is in the northeast corner of the map, on the south side of the bay with the Catch-A-Boat on the west shore, just behind one of the furnaces used to spawn Dexiduous the Invincible. This pool will also yield three fish.
The third pool is in the southwest corner of the map, just to the west of the large gorge with the elevator. This pool will yield four fish. Players are warned by the map boundary turret when they move out of bounds, but the furthest fish in the pool can be retrieved without characters having to move into the kill zone.