Blue Springs

Niebieskie Zrodla are a group of karst springs in the Pilica valley where water that has travelled through Jurassic limestone comes up into a set of shallow pools at a rate of several hundred litres a second, at a constant temperature of around nine degrees year round - which means they do not freeze in winter and steam in cold weather. The water is exceptionally clear, and because it is rising rather than standing, the sand on the bottom of the main pools is in constant motion, boiling up in patches where the flow comes through, which is the thing to watch. The blue is not pigment: it is the effect of the depth and the clarity scattering light, and it changes with the season and the sun. A boardwalk loop of about a kilometre runs round the pools and through alder carr, with an educational pavilion. It is a small reserve on the edge of a town and takes two hours.

What you actually see

• Sand boiling on the bottom - the flow visibly moving the bed in the main pools.
• A constant nine degrees - the springs never freezing and steaming in winter.
• Colour from clarity - the blue produced by depth and light, not pigment.
• A kilometre of boardwalk - a loop round the pools and through alder carr.

When to go

April to October for colour; winter for steam. Two hours.

Honest expectations

The colour depends on sun and is much weaker in cloud. It is small - two hours covers it. The boardwalk is the only permitted route. A small fee applies and it closes in the evening.

Nearby

Tomaszow Mazowiecki is beside it; the Pilica valley runs north.