If you have fished foul water in reapers march, then you know there are only 5 foul holes in the entire zone, and you need to run back and forth each time you deplete one.
Or if that isn't proof enough, Cyrodiil ocean has only 5 ocean holes aswell.

Im 100% certain that the game is always meant to have atleast 1 of each type of water hole up at any time in any zone, but it appears to be bugged in hew's bane when it comes to foul water. I've searched the entire zone, every building, delve, even the heists to try and find any hidden foul water holes but no, all i find are the same foul holes everyone else knowns about. @ZOS_GinaBruno @ZOS_ZebCook Zeb i know you are the zone lead, and i also am not sure if this is your area, but if you could inform the right guy to take a look/fix it, on behalf of every fisher i would thank you for saving us hours of wasting time waiting on holes to respawn