these are steps you may take for the purpose of solving the aforementioned problems:
1. photograph the event if possible;
2. Write a brief statement about the event and describe as precisely as possible how to arrive to the location (if there is a correct address, some visible object, distinctive sign and the like.)
3. Immediately report any suspicious act independently to the Water Rights Inspection Service, Hrvatske vode, Croatian Institute of Public Health, sanitary inspection (for biological analysis of water in case of discharge of sewage or septic tanks emptying into streams, rivers, lakes, and the sea), water-guards (who are in charge in Hrvatske vode for issuing an order for removal of waste from streams, rivers, lakes, and the sea) or call the telephone number 112 (National Protection and Rescue Directorate) where an employee who receives your call will promptly notify territorially competent inspection services which will take the necessary protective measures.

WHOM TO CALL: and/or Green Phone service for your county (072 123 456) - the report may be sent anonymously, too.
NOTE: You can always call the service 112, especially if it is a matter of great urgency, and during the weekends, holidays or at night