Blackwater Invocation( Stormwrack, p. 91)
You can call upon negative energy to infuse normal water around you, transforming it into the dark, cold water found at the bottom of deepest ocean trenches. This feat is favored by the clerics of wicked sea gods and the masters of the deep pelagic abysses.
Ability to channel negative energy,
By expending a daily rebuke undead attempt, you can infuse the water around you for a 30-foot radius with negative energy. The water darkens and becomes bitterly cold for 10 minutes. Those entering the water who are not protected from cold must make a DC 15 Fortitude save or take 1d6 nonlethal damage. This damage is the same kind of damage dealt by cold weather and is only taken once (as it would have to last a full hour to deal damage again). However, those leaving the area and then returning to it must make another saving throw or take further damage, since their warmed bodies are chilled once again. Those wearing warm clothing or otherwise protected from the cold (whether by any amount of resistance to cold or the endure elements spell) take no damage from this effect. Additionally, those within the area of affected water gain concealment. Those with the ability to channel negative energy are immune to the cold effects of this feat but are still subject to its concealment miss chance.