Trident of Fish Command

Source: D&D 5.2 SRD Magic Items

Weapon (Trident), Uncommon (Requires Attunement)

This magic weapon has 3 charges, and it regains 1d3 expended charges daily at dawn. While you carry it, you can expend 1 charge to cast Dominate Beast (save DC 15) from it on a Beast that has a Swim Speed.