JOLIET, Ill. (CBS) — New figures seem to support the argument that new casinos cannibalize the profits of existing ones.

As WBBM Newsradio’s Regine Schlesinger reports, until recently, the Grand Victoria Casino in Elgin was the state’s biggest moneymaker.

LISTEN: WBBM Newsradio’s Regine Schlesinger reports

But since Rivers Casino opened not far away in Des Plaines, revenues at the Grand Victoria were down 24 percent in August, to $18.5 million.

Two casinos in Joliet – Harrah’s and Hollywood Casino – have also lost revenues since Rivers opened.

Harrah’s Joliet generated $17 million, down from $20.2 million in August 2010 and $18.9 million in July. Hollywood Casino Joliet generated $11.2 million, down from $12.2 million in August 2010 and $13 million in July.

Rivers Casino generated $34 million worth of gambling business in August. The casino opened in late July.

The impact of the losses at Harrah’s and Hollywood Casino on city revenues for Joliet in August was worse than the city projected. But so far this year, city casino taxes have exceeded expectations as budget makers braced for the combined impact of a weak economy and more competition in the marketplace.

“For the month, we were about $135,000 short (of projections),” said Kenneth Mihelich, the city’s budget director. “For the year, we’re still about $500,000 to the good.”

Mihelich said he was “cautiously optimistic” that the city would end the year with more casino tax dollars than predicted in its budget.

Joliet officials, however, also are worried about pending legislation that would add new casinos within the Chicago city limits and in Lake County, the southern suburbs, Rockford and Danville, while also adding slot machines at horse racetracks and O’Hare and Midway international airports.

“I think what the numbers are showing is that the new business merely cannibalizes the existing market and just shifts dollars from one casino in the state to another,” Thanas said.

A parliamentary maneuver has kept the gambling expansion legislation from reaching Gov. Pat Quinn’s desk, despite approval by the Illinois General Assembly. Although he has yet to say outright if he would veto the legislation or amend it, the governor has called it “top-heavy” and indicated it needs a re-write.

The Joliet Herald-News contributed to this report, via the Sun-Times Media Wire.