There are statutes in most states, and certainly within the EPA, that deal with "chemical trespass". These statutes relate to the intentional, accidental or negligent use of pesticides - where same are allowed to enter another person's property, whether or not damage is documented.
Ranger's assessments of IL state agencies notwithstanding, the IDOA would be an appropriate agency to contact should several fish mysteriously turn up floating. The IDOA has the responsibility and authority to investigate any alleged pesticide misuses, including access to area pesticide dealers' sales records.
Here's a link for more info:
IDOA Drift Complaints
