Foraging watercress…the raw facts you need to know

Foraging watercress to eat raw in Britain? What you need to know about liver fluke…

Type in ‘Foraging watercress’ in any search engine and you may find websites either advising against picking watercress from the wild, or telling you how it needs to be cooked to be safe. The first statement can be dismissed as a scare story, while the latter only tells some of the truth.

This article hopes to shed more light on what remains a contentious issue amongst foragers here in UK. The question of whether to eat watercress raw from the wild.

You may think “what’s the point of taking the risk”, especially when cooking the plant kills the parasite, and the plant is freely available in supermarkets, but field grown, sometimes nitrate soaked watercress is bland and it disinterests me.

More importantly, I am seeking the maximum health benefits from wild herbs. With this one, like other pungent plants, including garlic, the medicinal goodness comes from the aromatic and flavoursome compounds that don’t survive cooking.

We will come to the icky parts of the liver fluke life-cycle and the dangers of contracting fasciolosis in due course, but firstly, how to identify watercress in the wild.

Botanical description to help identification when foraging watercress.

When foraging watercress you will find it growing by or in flowing water, typically appearing as a mass of stems
Watercress as will be commonly seen; a mass of stems and leaves in flowing water.

Watercress is a glossy-looking, mostly hairless, medium-sized, aquatic or sub aquatic perennial plant.  It has alternate, compound-pinnate leaves, typically with 7-9 oval shaped leaflets per leaf. The terminal leaflet is usually larger than the lateral ones.

Identifying brassica plants usually only takes a quick sniff. Their unique smell is one of their plant patterns. The majority of the plants in the family are pungent with a peppery, mustard-like or sulphurous tone, which will be easily revealed by crushing a leaf. So when foraging watercress, and in the right habitat, you can quickly discover if you have the right plant.

The stems are hollow and almost circular-shaped with ridges. Numerous rooting hairs are found just below the waterline. Water-loving plants adapted to submerged life contain large air-filled cells; a similar tactic to estuary plants.  At the base of the stems are a mass of fibrous white roots.

Watercress flowers first appear as mini broccoli type heads
Watercress flowers first appear as mini broccoli-type heads

This plant often grows in dense patches, so much so that it is classed as an invasive weed in some countries. In flower it can reach about 1m in height. It’s inflorescence will be a typical brassica display, appearing at first like a small broccoli-type head.

Soon after budding it will reveal numerous small white flowers, approximately 10 mm across. The four petals, like all cruciferous plants, are arranged in the shape of a cross.

Flowers soon give way to long thin seed pods, similar to numerous other related species. These spiral up the flower stem, eventually split to release their two rows of small red-brown seeds.

For more information on its botany and its global distribution, you may want to use this useful online fact sheet. For UK foragers, the online flora of Britain and Ireland contains useful distribution maps.

Habitats to look in when foraging watercress

Watercress grows alongside streams, ditches, springs and rivers, although won’t be found in stagnant water. It has a preference for alkaline soils, such as limestone or chalk.  This is a plant you will almost exclusively find in the countryside, although the more unspoilt parts of larger towns may also harbour some. My urban foraging guide may be of use here.

Watercress is known for overwintering  and therefore can be harvested at any time of year. This makes it another plant that comes high on my list of top plants to harvest, especially during the less verdant autumn and winter months. A general guide to the do’s and don’t’s of harvesting wild plants can be found right here.

Dangers of contracting liver fluke from foraging watercress.

Firstly, yes it goes without saying that waterborne plants such as watercress can potentially be infected with the cysts of liver fluke.  However, they will only be on the parts that are below the waterline, and this will realistically only be a problem on the plants near the edges in slow moving water, adjacent to damp grasslands. This is because of the life-cycle and host requirements of the parasitic organism.

So, let’s take a look at the life cycle of liver fluke (Fasciola hepatica). In the diagram below, you will see that the sheep contracts the cysts by eating infected grass. The cysts develop into the adult fluke which then lays eggs in around three months time, and these  will be deposited in manure. The fluke can lay thousands of eggs every week.

The Liver fluke cycle


The snail host of liver fluke

The eggs hatch into the first of a few embryonic and larval stages. If suitable environment conditions exist, such as prolonged damp weather, warm temperatures and a suitable wetland habitat, they can quickly find and enter the freshwater snail species – Galba trunculata.

Inside the snail host, the larvae will undergo more developmental changes until leaving and attaching to vegetation. Cysts are just about able to be seen by the naked eye, and more easily with a small magnification lens.


If we or our livestock eat vegetation with cysts on, then in a few weeks the adult liver fluke will be consuming our blood, possibly blocking the bile ducts and ruining  our livers, as shown below.

Cow liver showing the adult fluke and damage to bile ducts

Because grass is a monocotyledon plant, with only one seed leaf, and a growing meristem at the base, the cysts will eventually be found to be ‘moving up’ the blade. Whereas on dicotyledon species such as watercress, and without a growing meristem at the base of the plant, the cysts will remain where they were deposited.

Numerous liver fluke cysts aggregating on grass leaf blades

This is why foraging watercress in fields with streams, and damp meadows where sheep or cattle are regularly grazing, potentially leaves you at risk.This is why I forage for watercress quite a distance above the waterline, mostly using the very tops.

But what are the actual risks for us here in Britain? How many people in the UK have contracted liver fluke from foraging watercress from the wild and eating it raw?


Well, evidence for cases in humans are extremely rare here, unlike in parts of Asia, China and Africa. In the 10 years to 2008, only 6 cases in the UK were recorded.

During the following year, with heightened surveillance after a large increase in livestock cases, 11 people were reported to have faciolosis in England. This mainly involved people from North African and Middle eastern countries with a tradition of chewing the imported stimulant plant khat (Cathula edulis).

It is likely that our pre-industrial revolution forefathers would have had more of an issue with liver fluke, because many more common folk were forced to forage to supplement meagre wages or their field grown sustenance crops.

Whatever the dangers are currently, recent studies conducted for the NHS show that with our wetter and warmer summers here in the UK, the possibility of fasciolosis infection could  rise.

As with many myths surrounding foraging here in Britain, and foraging watercress in particular, the endless echo chamber of social media serves to inflate and hype any real dangers, with myriad keyboard ‘experts’ telling people not to pick wild stuff and certainly never to eat it. I have been told on more than one occasion by watercress growers and sellers at markets how dangerous it is!

Watermint grows in similar places to watercress, so could harbour liver fluke
Watermint is another sub-aquatic plant you may find when foraging watercress

Yet watermint will also be found in similar habitats, so I wonder why I can’t find many reports online about the dangers that this plant may bring, aside that is, from the odd well informed foraging website I visit.

Essentially, the rule not to eat watercress raw, could logically be extended to a large number of plants that live near waterways and the water’s edge, but the reality is that its hardly ever discussed amongst foragers online.

I have eaten plenty of raw wild watercress, especially over the last ten years, albeit from reasonably fast moving water, as found on rivers such as the Thames in Oxfordshire and the Avon in Somerset and Wiltshire, and having taken note of the improbable chances that cysts will be present in such conditions.

I always take leaves from well above the waterline, for reasons given earlier. Common sense is my best friend when out foraging, alongside arming myself with facts, not heresay!

I want the health promoting neutraceutical compounds that are now under investigation by pharmaceutical companies, and I continually weigh up the risks in the area I’m picking, with the risks of me smoking tobacco, occasionally drinking coffee and regularly enjoying  alcohol.

So although not recommending you go pick and eat raw watercress willy nilly, I do encourage you to take greater note of your local environment, assess the real dangers present, given what else you can find out about the local agricultural practices, and learn to decide for yourself what and where is safe.

Watercress is a much loved vegetable, and rightly so. There are many ways to use this tasty herb, such as this quick and easy-to-make soup, for which a recipe will be found on the wild food recipe page. Meanwhile…Happy foraging!


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