Your creature would have to release a massive amount of substances in the water.
A glue like substance soluble in water is the basis, e.g.
Then, in order to maintain the soft viscosity and reduce stickyness, add
How your creature would produce (or gather?) these substances, I don't know. But I think the amount of "excretion" needed will certainly limit the amount of water affected. The slime emitted would become a mantle around the creature, rather than extend far into the surrounding water.
It won't extend far. In order to affect all water around it, your beast would have to turn a relevant part of its own volume into slime. Slime consists of 90% water, so there would be at least 10% of substance weight that would have to be released into the water.
Note: in Earth's nature, some animals release defensive substances into the water. Octopus can do that, blinding the attacker.