It is a strong-smelling mint with large flowerheads comprising of two-lipped lilac-pink petals and crimson sepals. The stems are reddish and hairy with leaves which are oval and coarsely toothed, and often have a reddish tinge. The flowers can grow up to 6mm long, and the plant up to 1m tall.
It flowers July to September. It is found at the edge of ponds, pools, ditches and lakes, often growing in the water. It is also found in marshes, swamps, and similar freshwater habitats. A native species, widespread and common throughout.
The flowers are a good source of nectar for insects, and the leaves a good food source for caterpillars. The plant also has various medicinal properties and culinary uses.