Bolt from Beyond

You carve forth a rift to the deep sea, summoning primordial power to strike enemies before you in a maelstrom of lightning and freezing water. It strikes in a 40-foot long and 10-feet wide line out from you in a direction you choose. Each creature in the line must make a Dexterity saving throw. A creature takes 3d6 lightning damage and 3d6 force damage on a failed save, or half as much damage on a successful one. 

If this attack strikes natural water it becomes electrically charged for 1 minute, dealing 1d6 lightning damage to every character who enters or starts it's turn in the water.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the lightning damage increases by 1d6 for each slot level above 3rd.