This is typical river rowing-boat, made of wood, you may see all over Croatian rivers. The local inhabitants use it for own transportation along and across the rivers, for fishing or as the gunning punt. It is not recommendable to use it without escort of the experienced locals.
In case you like bird watching, especially the storks, there are plenty locations for that activitie in the surroundings of Sisak. Most of them are nature protected areas where hunting is not allowed.
To get to those areas, you'll have to take the local ferry-boat at Graduša Posavska.