Pennywort Status

For a detailed log of current pennywort status click here

The maps below show the status of pennywort on the Upper Cam at the year end (December).  Zoom into map and click on markers for more detail. (Note that the maps only show the status of floating pennywort above Jesus Lock, Cambridge. We started to work on eradicating it below Jesus Lock during 2019 and are making good progress)

See map key at the bottom of this page here

2022 Summary Report

Above Cambridge the river seems almost entirely pennywort free, although we suspect there may be some lurking in Grantchester Mill Pond. A few strands remain in the Shelford Award Stream, and on The Rush, and it will be important to keep an eye on these spots.

Downstream of Cambridge,  we have largely eradicated it above Baits Bite Lock, although clumps remained at Fen Ditton.  Between Baits Bite Lock and Bottisham Lock, we’re making progress. Further downstream, outside our area of activity, it was so horrendous they had to cancel a boat race.

2021 Summary Report 

We have successfully eradicated Floating Pennywort from the upper Cam. Above Cambridge the river is pennywort free. Just a few stands remain in the Shelford Award Street, and on the big bend on The Rush (a small stream in the center of Cambridge), and it will be important to keep an eye on these spots during 2022

2020 Summary Report 

This year Upper Cam appeared totally pennywort free, from Byrons Pool and Grantchester Mill Pond to Bishops Mill (ie opposite Scudamores, Mill Lane), apart from a small fragment removed from Grantchester Mill Pond in February 2020.  We should continue checking in 2021, but we appear to have eradicated Floating Pennywort from the upper river. It has been 3 years since we started significant eradication efforts, so this is a major achievement

However the nearby discoveries (and clearance) of significant infestations at the Shelford Award Watercourse (reported to us by the Environment Agency), Granta Moorings (reported to us by Cam Conservators) and a small outbreak in The Rush (spotted by us) shows that vigilance remains important.

Down stream of Cambridge’s Jesus Lock the situation is much more difficult.   Fen Ditton Ditch is nominally clear, wiith only a few small strands found during the year, but still needs monitoring. Downstream of Baits Bite lock, the Floating Pennywort remains out of control, with major infestations in side ditches.  Unfortunately due to Covid-19 it has not been possible to organise CVF working parties to help Cam Conservators tackle it.


Further dramatic improvements on the upper river, thanks to vigilance by a number of volunteers on the bank and in canoes, who pick up the occasional fragments as they appear and hence stop them growing and spreading.  Floating Pennywort is now rare, although we will need to remain vigilent in 2020 at the hotspots of Grantchester Mill Pond, Swan Island ditch and downstream past Paradise Island and Paradise LNR to snobs stream.  There was a small patch in the privately owned wetlands opposite Red Lion Meadow. This has been removed but will need monitoring by authorised volunteers


Dramatic improvement in the pennywort situation, thanks to intensive work by contractor and volunteers during 2018. Small hotspots remain at Grantchester Mill Pond, Swan Island ditch and Snobs Stream, but otherwise there’s no visible pennywort at the year end.  We’ll need to remain vigilant in 2019 though, especially once the growing season starts, to make sure we haven’t missed any, and to complete the eradication in the hotspots



Chilling video of kayakers pushing through the pennywort at pinch point 2 on upper Cam on 4 Dec 2016

Map key:

Turquoise: Clear of floating pennywort at year end, but present during the year.
Orange: Occasional patches of floating pennywort.
Red: Frequent or continuous mats of floating pennywort.
Black markers: Completely covered by floating pennywort, at least once during the year.
Turquoise markers: Upper limit of floating pennywort.

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