So what creates the drag force? What are you dragging against? If you are not swimming or dragging on the bottom or something else you will rapidly reach water speed. It doesn't matter if you are a tiny piece of seaweed or a dead whale.you aren't moving faster than the current, just at a higher proportion of the current speed than a less streamlined diver.
you reach an equilibrium between the normal force of the current against drag force to determine the steady state velocity.
maybe terminal velocity isnt the right term