First time playing (2017)

I was playing ark with my brother on the island and we were trying our best to explore and discover the map and we tried to cross a small river on the bottom left side of the map and all of a sudden we were dying and we had no clue why until I dove under and found out a swarm of piranhas were killing us over and over again.

Returned a few weeks later with a spinosaurs and tore through them... vengeance was finally mine