The idea of introducing the beaver into Croatia appeared in 1990 and 1991 during the work on the project "The beaver in Bavaria" and it very soon turned into a project. Knowledge of beavers living in these parts up to the end of the 19th century allowed us to speak of renaturalization or reintroduction of the beaver into Croatia. Besides, this information facilitated exploration of habitat conditions for the beaver because, if beavers used to live here and if the habitats have been preserved in their natural form, there is no reason why they would not provide good living conditions for the beaver today.
After the idea was presented and the green light for further activities obtained, search was started for an area suitable for the naturalization of beavers, that is, potential beaver habitats were explored.
The first steps involved definition of a wider area containing potential beaver habitats. After studying the wider area to the east of Zagreb, using geographical maps, two areas were chosen for further research. These areas are situated in the Zagreb-Sisak-Kutina triangle and along the River Drava from Donja Dubrava to the point where it is joined by its tributary Velika Čambina. As part of preliminary explorations, fifteen localities were inspected in these areas and they were immediately appraised on the basis of the main site characteristics. Of all the localities, two were selected as the most suitable habitats for beavers: Zutica near Ivanić Grad and the Drava by-channels in the vicinity of Legrad. Detailed investigations of these localities provided information on the vegetation composition on river banks and in the adjacent area, as the basis for food, seclusion and shelter. The vegetation, with prevalence of soft deciduous woody species, bushes and herbaceous plants, offers the right habitat conditions for the beaver.
Potentials for beavers spreading over the adjacent area as well as adequate locations for lairs and stabilization of the population make these sites even more attractive. Investigations aimed at establishing water level fluctuations should supply data on the water level of the streams that provide the habitat conditions required by the beaver. High water waves are characteristic of all natural watercourses and the animal species living near them are adapted to such natural rhythm. To facilitate the existence of the beaver population, it is desirable that water level extremes should not coincide with the time of littering and bringing up of young beavers.
Data on long-term daily water level readings for the streams Česma, Lonja and Drava show regular occurrences of water level extremes, which fortunately fall outside the period that is critical for beavers. It is additionally encouraging for project implementation that the otter, which resembles the beaver in its habitat requirements, is found in the chosen area.
Based on the site characteristics studied, which have confirmed their quality, a programme has been designed for naturalization, that is, reintroduction, of the beaver into Croatia.
The investigation results obtained represent the outcome of the preparatory stage for project implementation.