Brinicle

You conjure a mass of extremely low temperature brine in a target location, instantly freezing and damaging anything that comes close. The salinity of this brine is three (3) to eight (8) times greater than normal open ocean water, making its freezing point as low as negative twenty-one (-21) degrees Celsius (-6* F), and making it toxic to all living creatures. 

When you target a location within range with a depth of at least 5 feet of water, an icy finger of brine reaches up to 15 feet in length (no higher than the surface of the water). As the icy brine flows, it instantly crystallizes the water around it. Each creature within 5 feet of the brinicle must make a Dexterity saving throw. A creature takes 8d10 cold damage on a failed save, or half as much damage on a successful one. On each of your turns until the spell ends, you can use your action to move the brinicle 15 feet and repeat the spell's saving throws. If any creature that has not been damaged by this spell since the start of your turn comes within 5 feet of the brinicle it must perform the saving throws as described. Any creature caught within the brinicle must make a Constitution saving throw or become paralyzed until the start of your next turn. Undead and constructs automatically pass the Constitution saving throw. If a creature is held within the brinicle for the entire duration of the spell (1 minute), failing every Constitution saving throw, the creature enters a state of toxic shock. When this happens, the creature is paralyzed for an hour and gains three (3) levels of exhaustion. 

When you target a location within range with a depth less than 5 feet of water, a 5 foot orb of pure liquid brine falls to the ground. Each creature within 5 feet of the spell's target location must make a Dexterity saving throw. A creature takes 4d10 cold damage ands falls prone on a failed save, or half as much damage on a successful one. Any creature caught within the brine itself when initially cast must make a Constitution saving throw or become paralyzed for 1 round. On each of your turns until the spell ends, you can use your action to move the brine up to 15 feet across the floor and damage a 15 foot diameter area. If any creature that has not been damaged by this spell since the start of your turn enters the area for any reason they must make the Dexterity saving throw. 

At Higher Levels. When you cast this spell using a spell slot of 6th or higher level, the damage increases by 1d10 for each slot level above 5th.