PHILADELPHIA — Gross revenue from slot machines was up 5.7 percent at Pennsylvania casinos last month as the state’s gambling industry continued to grow, but there were signs of the effects of new competition from neighboring Ohio.

Monthly revenue figures released Wednesday by the Pennsylvania Gaming Control Board showed the state’s 11 casinos generated gross revenue of $210.6 million in August, an increase over $199.2 million in August 2011.

This year’s figures were boosted by play at Valley Forge Casino Resort, which opened in March and brought in nearly $4 million from slots last month. Gross revenue was up 3.7 percent when looking solely at casinos that were open in August 2011.

Six of the casinos showed August year-over-year gains, led by a 14.4 percent increase at Sands Casino Resort in Bethlehem, an 11.8 percent increase at Sugarhouse Casino in Philadelphia and a 13.3 percent increase at Mount Airy Casino Resort in northeastern Pennsylvania.

Four casinos showed declines, with the biggest drop at Presque Isle Downs and Casino in Erie, near the Ohio border. That casino is facing new competition from Horseshoe Casino Cleveland, Ohio’s first, which opened in May. Last month, Presque Isle’s gross revenue from slots was down 9.2 percent, with $13.4 million in gross revenue compared to $14.7 million in August 2011.

Three other casinos saw less notable declines. In central Pennsylvania, the Meadows Racetrack and Casino was down just less than 4 percent and Hollywood Casino at Penn National Racecourse was down less than 1 percent; in the northeastern part of the state, Mohegan Sun at Pocono Downs was down 3.2 percent.