How does underwater rules work with flying familiars?


I will soon run the Underworld Speculation adventure with my group of players and two of them have flying familiars. An owl and a pseudo dragon.

Is there something in the rules that states that a familiar or a flying familiar can’t be used in water ?

There isn’t any rule change or anything about underwater fight and exploration. PC group is able to breath underwater thanks to a NPC that casts Water Breathing.