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Zdjęcie Cieszyna

The Olza River

The Olza River

The Olza River is an important river for our region. Its spring is located on the Polish side in the territory of the Kamesznica district in the Silesian Beskids; it joins the Odra River after the 99th kilometre, near Bohumín, at an altitude of 190 meters above sea level. The 25.3-kilometre-long river forms the border between Poland and the Czech Republic. It is used mostly by birds and water animals for migration. The river banks are green in the territory of the town – along the Mír embankments on the Czech side and in Adam Sikora Park, where old trees which are very scarce in this region can be found. As a result, we can find not only common species here, but also some rare or endangered animals. The river administrator is a state-owned company called Povodí Odry. A lot has been written about the river, as it is closely associated with the life of our region. It even became the main character of the book entitled “Olza od źródła po ujście”.


Eurasian kingfisher

For its nesting location the bird chooses clay banks which are located in more natural, untouched sections of the river. Kingfishers feed on small fish and can be seen on the river and in the territory of Cieszyn, sitting on guard rails or branches above the water surface and catching fish. The kingfisher has a characteristic whistle, which makes the bird easy to identify. Due to its beautiful plumage, it is also called a “flying jewel”.



The Olza and the Odra rivers are among the most important nesting places of this northern duck in the Czech Republic. This once rare and skittish species, which only wintered in our country, has become so common that it started to inhabit also urban areas. Goosanders can be regularly spotted by observers walking near the river, and they even choose hollows of old trees as their nests.



Mallards spend the whole year on the river and regularly nest here. In the town they can usually be found under the Liberty Bridge, i.e. at the end of Strzelnicza Street; it is where they are often fed by locals. Some unusually coloured specimens can also be identified among these birds. They include mallards of all description, which were bred in captivity and escaped from a farm to nature. However, they are not welcome there, as they may distort the behaviour of the rest of the wild population.


Mute swan

Every year the river becomes a wintering location for a few swans. Sometimes these beautiful birds appear also in the town, most often near the Liberty Bridge at Strzelecka Street. They are often found in non-frozen parts of the river, under the sewage treatment plant in Kocobędz. The residents often fear that during severe frosts swans will freeze to the ice, but research conducted by ornithologists has shown that the birds are able to cope with frost quite well.


Great cormorant

An important winter habitat for this species in the past was the territory of Třinec Iron and Steel Works and its neighbouring areas. As many as hundreds of specimens spent winter there. Their maximum recorded number was around 700. In recent years cormorants have been appearing here only occasionally, in groups of not more than a few dozen.


White-throated dipper

The dipper is an amazing hunter. Contrary to other Passeriformes, white-throated dippers can dive and pick various invertebrates from the river bed. They are not afraid of diving even in severe frosts. They regularly nest at the confluence of the Ropičanka and the Olza rivers.


Grey wagtail

It is impossible not to notice the characteristic bird with a yellow belly, a long tail which it often moves. It sings, making specific sounds. It usually searches for food on stones above the water and sometimes likes to sit on the bridge guard rails for a long time.


European beaver

Beavers have been inhabiting the neighbourhood of Cieszyn for a few years already, although they can rarely be seen in the town, usually when swimming through it at night.  The signs of the beaver’s presence can be found in cut willows on the waterside or gnawed trunks. Such signs can be found along the river on the section between Cieszyn and Karviná.


European otter

It is a permanent resident of the river and its tributaries. It also appears in smaller reservoirs. While it used to be a relatively rare species, it can be seen quite often today. The greatest danger faced by otters are sluices and bridges that are an insurmountable obstacle for them to swim through and force the animals to walk across the streets, often resulting in accidents. However, otters can be spotted quite rarely, as they usually travel at dusk and at night. Their presence becomes most noticeable in winter in the form of animal tracks on the snow and faeces on stones.


Daubenton's bat

It is the most characteristic species of bat. The Daubenton’s bat most often dwells in hollows of old trees from which it flies out after dusk. In warm spring and summer evenings you can observe bats flying low above the water. They most often hunt insects that fly above the surface of the water, sometimes catching them just above it. You may sometimes spot bats near the pond in Adam Sikora Park.


Beautiful demoiselle and banded demoiselle

These graceful, characteristic dragonflies appear above the water at the end of spring and beginning of summer. In warm and sunny days they fly over the river and often sit on various kinds of plants on river banks or stones.


Azure damselfly

These small dragonflies can be observed by a small pond in the park near Sikorák restaurant. A few species can be found here, including the common blue damselfly, the large red damselfly, the blue-tailed damselfly or the rarer species of small red-eyed damselfly.


Collared flycatcher

This beautifully coloured black and white bird of the order Passeriformes likes to dwell in hollows of old trees, but it can as well set up its home in a birdhouse. It nests in a few places in the park, and one pair inhabits even a birdhouse by the playground. Flycatchers can be easily recognised, especially in May when they sing. Later they become less active and are hard to notice in thick tree crowns.


Horse-chestnut leaf miner

This small butterfly lays eggs on chestnut leaves; after the caterpillars hatch, they start to feed on the tissue of leaves, which soon dry out and fall. So far no cases of total tree destruction caused by chestnut leaf miners have been reported in our region, although the caterpillars feeding on them make them significantly weaker. In 2015 the town began to vaccinate chestnuts using a special substance which considerably reduced the attacks of chestnut leaf miners on majority of trees. What is more, great tits and Eurasian blue tits which feed on chestnut leaf miner larvae have been spotted in the park. As it turns out, the leaf miner has its natural enemies, too.


Perfidious fungus and insatiable beetle

Virtually all ashes in the territory of the town have been attacked by the fungus called Chalara fraxinea which gradually leads to the dying out of the trees. It is manifested in the drying out of end branches, which is soon followed by the whole tree. Trees weakened by the fungus fall victim to beetles of the Hylesinus fraxini and Hylesinus crenatus species, which belong to the group of bark beetles. The presence of those beetles can be recognised by the characteristic holes in branches or tree trunks. The most affected trees in our town are gradually removed and replaced with other species.


Erpobdella octoculata

This tiny leech lives in the water under stones. It does not pose any danger to people – it does not drink blood and it feeds on small water animals. It is one of the most common species of leech in our region. Adult specimens can be found in the river, and in spring months even the entire brown cocoons attached from below to the stones can be found there.



Sometimes oval pipes built from tiny stones or plant waste can be found under stones. These are nests of caddisfly larvae which the insects use as their shelter. The biggest danger for caddisflies is contaminated water and night lighting in the areas near watercourses. Adult specimens often fly up to the light sources and die. Caddisflies constitute essential food for fish.


Stoneflies and mayflies

Larvae of both orders can be found in the river under stones, and adult specimens sometimes appear in the areas near the river. They constitute essential food for fish and are indicators of water cleanliness. As a result of watercourse contamination, many orders are becoming less and less common, and for this reason, they have been included in the list of endangered species.



The river is home to many species of fish, among which the alpine bullhead is one of the rarest, while the group of most frequent inhabitants include the common nase, the grayling, the trout and the chub. Fish are controlled by the Czech Fishing Association.


Hummingbird hawk-moth

In summer months it flies around flowers and drinks nectar with a long sucker, often hovering in the air and fluttering its wings very fast like a hummingbird. It regularly appears e.g. near geraniums that decorate the market square.



This bug appears in spring and summer months mainly on linden tree trunks. There are days when even hundreds of them can be spotted. Their largest concentration is found in Adam Sikora park on lindens around the pond. The bugs do not pose any risk to trees.


Shaggy scalycap

The characteristic, decorative mushroom which grows mainly in autumn on dead wood or at the foot of tree trunks. It parasitizes the tree root system, clearly reducing its strength, which significantly lowers the stability of the trees. In parks it mainly appears on ashes.


Grass snake

This most common snake in our region lives near the water, and it can be recognised thanks to two yellow spots at the back of its head.  It can sometimes be seen in a pond in Adam Sikora Park or along the entire embankment. It hunts a variety of small water animals. The snake is not venomous and it does not attack humans, nevertheless, it is recommended not to catch it, as it secrets a substance with a strong smell, which is hard to wash off clothes.



It parasitizes deciduous trees, especially small-leaved limes. Over the last several decades it has been attacking trees so intensively that it causes their gradual withering. It is mainly spread by birds from the family of thrushes, for which it is an important nutrient. It is a medicinal plant with mythological significance.


Rats and mice

They reproduce mainly at dumps containing waste from nearby fruit and vegetable gardens set up by irresponsible residents on the banks of the watercourses. The phenomenon mostly affects small watercourses.

Projekt dofinansowany przez Unię Europejską ze środków
Europejskiego Funduszu Rozwoju Regionalnego
 w ramach Programu Interreg V-A Republika Czeska – Polska