15 June 2016 Last updated at 18:31 BST
But patrols by international naval forces have made them much safer.
This is good news for fishermen in the self-declared republic of Somaliland.
BBC Monitoring's Africa security correspondent Tomi Oladipo reports that they hope it will prove a lucrative source of revenue in the future.
The waters around the Horn of Africa were among the world's most dangerous a few years ago because of frequent pirate attacks.