Osijek and its surrounds were heavily laid with landmines during the war in the 1990s. Although the city and its outskirts along the main road have been de-mined and are completely safe, it would be unwise to wander through the swampland north of the Drava River, which leads to Kopački Rit. Most mined areas are marked; be on the lookout for signs.
In summer, Kopački Rit is besieged by mosquitoes. Wear long sleeves and trousers or slather on plenty of repellent.