A control system governs fluid level in a well system including a pump positioned downhole for pumping fluid upward through a tubular, a rod positioned within the tubular for driving the pump, a prime mover, and a pumpjack to transmit power from the prime mover to the rod to reciprocate the rod. A sensor senses a position of the rod or a member of the pumpjack and outputting signals in response thereto. A controller receives the signals and computes a plurality of time intervals, each time interval being between signals and occurring during at least a portion of an upstroke of the rod. The controller selectively decreases power output from the prime mover in response to an increase in the computed time interval.