In the 1940s the watershed further up the Don River became more urbanized. This caused an increasing amount of silt to flow down the river. The silt collects in the channel where there is very little water flow. Since that time, the Toronto and Region Conservation Authority (TRCA) has been dredging the channel. The dredgeate material is barged out to the Leslie Street Spit where it is dumped in a containment area built for this purpose. In 2005, the annual amount of silt dredged was about 35,000 cubic metres. The containment area has the capacity to take 50 years of Don River dredgeate [https://web.archive.org/web/20060417082711/http://www.trca.on.ca/water_protection/don_mouth/default.asp?load=key_study].