Foraging for swimmers: watercress

Offering a gentle rendition of wasabi’s heat, watercress (Nasturtium officinale) is one of the oldest known leaf vegetables consumed by humans. Susanne Masters has your guide to this wild-growing superfood. 

Offering a gentle rendition of wasabi’s heat, watercress (Nasturtium officinale) is a wild-growing superfood. Wasabi, watercress and other members of the cabbage family are characterised by glucosinolates, sulphur and nitrogen-containing compounds, which we experience as hot, pungent and sometimes sulphurous tastes. Referring to watercress as a superfood isn’t just considering its nutritional benefits, but also its role as a ‘food for free’ that grows with abundance.

If you are tempted to swim for your supper, alongside the standard codicil of being able to correctly identify the plant, you must use local ecological knowledge. Watercress is a host for sheep liver fluke. Leaves that are submerged underwater or have been submerged can carry cysts for the plant stage of this liver fluke’s life cycle. Flukes will inhabit the liver of the animal host, human or sheep, which has consumed them raw. Cooking kills liver flukes rendering them harmless. If you want to eat wild watercress raw you must be sure that there are no sheep upstream from where you are picking it and be familiar enough with water height to know leaves have not been submerged.

All aboard the Watercress Line

Appetite for watercress was big enough to shape transport infrastructure. In Hampshire the Watercress Line was established in the 1860s to connect commercial watercress growing in Alresford with markets in London and Southampton. Now if you buy watercress in a supermarket it is often marked as produce from Spain, and shipped in from the Canary Islands. 

Tenerife and Gran Canaria have something in common with Hampshire: springs supplying crystal clear, well-oxygenated water. If you order sopa de berros in the Canary Islands it won’t be green and pureed English-style, although the words mean watercress soup. In the Canary Islands watercress soup is more like a stew, containing large pieces of watercress.

Where to find it

Watercress grows in shallow, fresh water. Swimming in chalk streams you are rarely far from watercress on stream edges and shallow patches midstream. It also pops up on beaches well above the tide line, where freshwater seeps down through cliffs, or streams run over the shore. Putting up leaves just before the surface flow of a winterbourne – an intermittent stream on chalk – resumes flow, watercress sprouts from seeds in the soil as it responds to rising subterranean water.

• River Wensum, Norfolk
• Afon Soch, Abersoch, Gwynedd
• Ballintoy, Co. Antrim
• Logan burn, between Loganlea and Glencorse reservoirs, Midlothian

Illustration: Alice Goodridge. This article is from the March 2023 issue of Outdoor Swimmer. Click here to subscribe to the magazine. Read more from the March edition.