Outer Limits 4x4 Board

hey just rememberd this, the 80amp fuse that sits inisdi the lil fuse box next to the battery on the right hand side right, it had a crack in the top of it and was out 4wding in mud and lots of water and im assuming water must of got inside of it because the engine light came on, the engine began to hesitate to rev and it stalled!! this happend all in about 30seconds!!! got out could smell electrical scent immedialtey and it ended up being THAT fuse , it had melted a small section of the fuse case and burnt 40mm of the cable that connects to it!!!

since then it has ran fine but should i replace this? even though it runs fine (besides the idling issue i had but fixed now)

also what is that fuse for???