An easement consisting of a baulk or beam usually made of wood or concrete being fixed across the face of the weir sloping downwards to the apron. Where the baulk meets the weir crest a notch is cut.

In combination, the notch and baulk create a channel of water across and over the weir through which fish can swim. Some of the weirs on the River Don have listed status and easements are a less invasive way of helping fish to ascend the weirs and a lower cost option.