This image only shows River, Ocean and Lake water, but no foul water spots. However I did find a "Foul Water" fishing spot in the lake located Southeast of Viridian Woods wayshrine, Southwest of Lakewatch Tower and Northeast of Summoner's Camp. Near the foul water fishing spot there is 1 dead troll, 4 dead Khajiit bodies on the ground near a boat and 2 Lamia creatures near a rock.

I'm not sure if that was a mistake or if it's suppose to be foul water ?