Both structures being contemplated for removal in Danville are low-head dams, which are less than 25 feet high and extend across the entire river channel. They are not flood-control dams but run-of-river, meaning they don't block the flow of water but slow it, creating a pool of water above them. The Vermilion River dam is 11 feet high, 240 feet long and was built in 1914 by Danville Street Railway and Light Co. Danville Alderman Bill Black said its purpose was to create a pool of water upstream that was used to cool the company's boilers at its generating plant. The Ellsworth Park dam was also used to create a pool upstream, but it was for recreational swimming, according to Black.
According to the state, most low-head dams in Illinois were typically built in the 19th and early 20th centuries to provide mechanical water power, and they have historically posed a public safety hazard throughout the country and Illinois, according to a 2007 report commissioned by the state of Illinois, documenting existing conditions and possible safety improvements at 25 run-of-river dams, including the Vermilion River dam.
In 2006 alone, there were several drowning deaths at low-head dams in Illinois, according to that report. There are no official, historical statistics on such incidents in Illinois, but anecdotal evidence suggests there are several incidents across Illinois at low-head dams each year, according to the report.