In time, Zasavica river was formed from the subterranean waters from the Drina and from several streams, most notably, Duboka Jovača and Prekopac canal [3] (gravitationally, from the Cer mountain).

The entire biotype includes also the Batar stream and several other canal-tributaries to Zasavica, and consists of an ecological row of water and marsh systems with fragments of flooded meadows and forests.

[4] From recent history, Zasavica is known as both the hiding place and a battle ground of Zeka Buljubaša, one of the heroes of the First Serbian Uprising.

[5] In 2017–2020, a dozen sculptures of the animals which inhabit the reserve were carved and exhibited in the open, including beaver, umbra fish and donkey.

Celebrating importance of oxen in older Serbian history, the sculpture was carved from one slab of hard, ancient Brazilian stone, formed over 1 billion years ago.

The majority of the protected area covers the water surfaces of the rivers and canals Zasavica, Jovac, Prekopac and Batar.

Several of them are endangered natural rarities and listed in the Serbia's Red Book of Endangered Species: European white water-lily, yellow waterlily, water soldier, fringed water-lily, marsh nettle, sweet flag, aquatic bladderwort, triangular club-rush, common mare's tail, water violet, greater spearwort and the endemic Pannonian plain species of Pannonian cornflower.

150 species of fungi are widely distributed in the entire reservation, in every ecosystem (ground, trees, logs, meadows, and pastures).

Although dozens of species of trees are found, the forests, which make up 16.74% of the reservation, mainly consist of narrow-leafed ash and to a lesser extent white poplar, willow, or black alder.

[4] Seven species are protected: Umbra krameri, Rhodeus sericeus amarus, loach (Misgumus fossilis), Cobitis tenia, etc.

Eurasian shrew, striped field mouse, fat dormouse and several species of bats are listed as rarities in Serbia.

They are kept for meat but mostly for their milk, which is used to make the pule cheese, one of the most expensive in the world with the price of 1,000 euros per kilogram (there are farms of the Balkan donkeys in Italy, Belgium and France with over 700 animals).

[8] Extinct in the early 1900s, four families with five members each, plus 11 single animals (31 in total) were reintroduced in 2004 with the help from the Bavarian Science Society.

As the area surrounding the Zasavica is entirely agricultural, farmers don't share the excitement of the biologists as they claim the beavers ruin their crops saying that was the original reason for their extinction a hundred years ago,[9] though they were also hunted for the valuable fur and the meat which could be consummated during the religious fasting.

[8] By 2012, beavers in Zasavica built 17 burrows and 6 dams, their population grew to a 100 and the chipped specimen have been caught near Šabac, Obrenovac and even Brčko, 135 kilometres (84 mi) upstream, in Bosnia and Herzegovina.

Population found in Obedska Bara is a local one, being reintroduced in the same time and as the part of the same project as the Zasavica beavers.

Initially knocking down the poplars and willows, causing damage to the surrounding arable land, after several years in which they adapted the habitat to their needs, beavers for the most part stopped being a nuisance to the local inhabitants.

Apart from the Sava, Drina, and Jadar, they have been spotted in the Danube, Tamnava, Tisza, Bega, Timiș, Great Morava and canal systems in the Vojvodina province.

[3] In 1998 Mangulica was introduced in Zasavica, but unlike Podolian cattle, they are left to roam free in the reservation, becoming feral since then.

[12] Breeding of Podolian cattle is being part of the program for the preservation of the animal species, developed by the Serbian Ministry of agriculture.

[4] In the reserve there are several other, today rare, breeds of domesticated animals: Buša cattle, Bosnian Mountain Horse and wooly goat.

[14] In March 2008 the fish was discovered in the village of Bački Monoštor, near the town of Sombor, almost 150 kilometers north of Zasavica.