Apologies to those who are very familiar with this pest (no, not me), but in case you're new to the river and haven't encountered it before, here's something to steer well clear of.
It looks a lot like Rhubarb, or maybe a cross between Rhubarb and the ornamental Gunnera Manicata that grows to such prodigious sizes, (and is sometimes called 'giant rhubarb'), but it's a lot more unpleasant than either.
Yes, it's Giant Hogweed (Heracleum mantegazzianum) and you'll see it soon on a riverbank near you, if you haven't already. It is growing fast (very fast) and spreading all along our beats. It's probably worse along Beat 3a for some reason (perhaps the shade) but if you look, you'll see loads of it. It can grow up to 3 metres high, and this pic was taken yesterday, so there are some already a metre high as well as lots of little ones.
It's an extremely nasty plant and you must be very careful not to touch it. It is phototoxic, so if you manage to get any sap on your skin, and expose it to daylight or sun (which is particularly strong at this time of year), it will blister very badly and quickly, and can cause a scar. If you do accidentally get any on your skin, wash it well with water immediately, cover up the skin, and consider seeking medical advice when you can.
Don't try to dispose of the plants yourself (it as classed as controlled waste).
The Environment Agency normally patrols the river around this time of year in an attempt to spray all the plants with weedkiller, though it's a mammoth task, and certainly some will be missed.
All you can do is watch out for it, be very careful if you pass near it, and whatever you do, don't waste good custard on it.
Cheers
PeterB