Static rejuvenation may also occur, in rare instances, when a downstream knickpoint erodes its way upstream to a lake which establishes base level for its tributaries. When the knickpoint reaches the lake, the lake drains, and the base level of upstream waters lowers rapidly from that of the (now former) lake to that of the river downstream of the knickpoint. At some point in the future, a quite dramatic example will appear when Niagara Falls cuts its way back to Lake Erie.