A technique to sample plankton efficiently in the fluvial systems is being propounded along with a note on the need and design of the plankton sampling device suited to torrential reaches. The technique, christened as discharge-time method, has certain advantages. The requirements are minimum (detachable bucket of the conical plankton net with bolting silk cloth of required mesh size) and the efforts are nominal. In order to sample plankton the device has to be dipped into the river with its open end facing the current, for a pre-calculated period of time. The formula, ‘t’ seconds=x/4v was computed to calculate the time for which the device should remain submerged. It is thus, an efficient and time saving technique for large volumes can be filtered within seconds. The validity of this method has been assessed by employing ‘t’ test.