A waste weir provides a means of removing excess water from the canal and provides a means of draining a section of the canal for repairs, for winter, or in anticipation of flooding. Because rising canal waters could overflow the banks, eroding them and causing a break in the canal, water weirs were and important safety feature. Also, high water in the canal could prevent canal boats from passing underneath the low bridges. (There were over 300 bridges over the canal.) Waste weirs were often located near feeder streams that might carry flood waters into the canal, and they often emptied extra (waste) water into existing streams.