DES MOINES, Iowa, June 24 -- The Iowa Department of Natural Resources issued the following news release: * * * Petroleum release near Avoca reaches West Nishnabotna River * AVOCA - The Iowa Department of Natural Resources is investigating a petroleum release at the West Nishnabotna River near Avoca in Pottawattamie County. On June 24, staff from the DNR's Atlantic Field Office observed a petroleum sheen entering the West Nishnabotna River, just north of the Avoca exit off Interstate 80.  more PR