Living up to its name, the bullhead has a characteristically large, flattened head and a tapering body. Look out for it in fast-flowing, stony rivers and streams.

The tiny, brown-and-white sand martin is a common summer visitor to the UK, nesting in colonies on rivers, lakes and flooded gravel pits. It returns to Africa in winter.

The silvery dace can be seen gathering in large shoals in lowland rivers and streams. It is a member of the carp family and looks very similar to the chub, but is smaller.

A handsome fish, the tench has olive-green flanks, powerful fins and distinctive red eyes. It can be found in lowland lakes and slow-flowing rivers around the UK.

As its name suggests, Water dock likes damp places, such as the egdes of canals, ponds and rivers. It is a tall plant with large, greenish flower spikes.

A fierce predator of small fish and flying insects, the brown trout is widespread in our freshwater rivers. It is has a golden body, flanked with pale-ringed, dark spots.

The Common clubtail is on the wing in spring and summer. It is an elusive dragonfly that is easiest to see when it first emerges. It can be found along rivers in Southern England and Wales.

As its name suggests, Himalayan balsam is from the Himalayas and was introduced here in 1839. It now an invasive weed of riverbanks and ditches, where it prevents native species from growing.