Una national park

The Living Landscape

Una National Park is internationally known for its so‑called tufa or travertine formations — natural limestone barriers that are still forming in real time. This means the landscape is not finished. It is a work in progress, where water, stone, and microscopic life slowly create new shapes before our eyes.

Here, nature is shaped not by machines or human hands, but by a precise interaction between chemistry, biology, and time.

What Do “Self‑Building” Limestone Formations Mean?

The Una River is rich in dissolved calcium carbonate. As the water flows over stones, roots, and plants, microorganisms — algae, mosses, and bacteria — attach themselves to the surfaces. These organisms act as natural filters that trap minerals.

Over time:

• Minerals accumulate around the microorganisms

• Layers build up gradually

• Soft deposits harden into porous limestone

The result is natural dams, terraces, small islands, and waterfalls.

This does not happen quickly. Often, the formations grow only a few millimeters per year — but the process never stops.

Every visit to Una reveals a landscape that is slowly changing.

A River System in Motion

Unlike many rivers where erosion breaks down the landscape, Una simultaneously builds new structures.

Over decades, this can lead to:

• New waterfalls forming
• Existing waterfalls becoming higher or wider
• The river’s channels slowly shifting direction

One of the clearest examples is Štrbački Buk, where multiple levels of waterfalls have gradually formed through tufa deposition.

This phenomenon is rare on a European scale.

An Extremely Sensitive Ecosystem

This type of limestone formation can only occur under very specific conditions:

• The water must be exceptionally clean
• The temperature must remain relatively stable

• The flow rate cannot change too drastically

Even small disturbances can stop the process entirely.

For example:

• Pollution from sewage or chemicals

• Increased sediment from erosion

• Stepping on fragile formations

When the microorganisms die, the limestone formation stops.

For this reason, large parts of Una National Park are strictly protected, and some areas may only be accessed via marked trails.

Biological Diversity

The clean river and constantly changing habitats support a rich variety of wildlife:

• Several fish species, including endemic species

• Amphibians and reptiles linked to wetlands
• Otters, deer, wild boar, and occasionally large predators in the forested areas

• A wide range of insects and aquatic organisms

Many small species are still poorly documented.

Research and Scientific Importance

Una is used as a reference area for studying:

• Natural travertine and limestone formation
• The relationship between microorganisms and geological processes
• How river systems respond to climate change

Despite decades of research, scientists still lack a complete understanding of all the chemical and biological mechanisms behind tufa formation.

This makes Una a living laboratory.

Why Una Is Unique

• One of the few places in Europe where tufa is still actively forming
• A landscape that is literally growing

• A combination of high biodiversity and ongoing geological processes

Una National Park shows how nature can be both creator and architect — without human intervention.