A full study of the canal was published in 1981. It indicated that on an average day, more than of raw sewage emptied into it. The report also documented the decreasing use of the canal by industry and shipping. The number of industrial firms using the canal fell from nearly fifty in 1942 to six in 1981. The amount of freight brought through the canal was more than 55% lower, and the number of times the drawbridge was opened declined by almost 70%. The report put forward a number of recommendations, one of which was fixing the flushing tunnel to increase the oxygen content of the water.