Squids won't spawn in River biome

This is a map I created around 3 years ago and I've been keeping it updated since then, I did this squid farm in a river biome and I made sure there wasn't more water around to avoid them to spawn elsewhere, but I still have got no squids spawning in here.

Later on, I went to another river not close to the squid form and the river was completely empty as well, looks like all the rivers around are empty, not even fishes...