Cowroast Lock and Marsworth Flight restrictions: what they mean for a day out from Cow Roast Marina
Cowroast Lock. Drawing adapted from a photo by Stephen McKay, and shared under the same licence, CC BY-SA 2.0.
From 2pm on Monday 5 October 2026, Cowroast Lock and the seven locks of the Marsworth Flight are open to boats from 10:00 to 14:00, with a final passage window at Marsworth until 15:00. The Canal & River Trust has put the hours in place to save water after rainfall well below average. The Trust's notice is titled a navigation closure, but its type is a restriction, and it says unnecessary movements may bring a full closure closer.
The notice sets hours for those two sets of locks. It lists none for the stretch of canal between them, the Tring summit, where our boats start. Day hire carries on, heading north on a route with no locks, and the Trust asks all boaters to "only navigate when absolutely necessary". This page explains what that means for the Tring canal and for a day out from Cow Roast Marina.
Last checked against the Trust's notice on 6 October 2026. The notice was last amended at 8:16am on 5 October, and the Trust will review it on 12 October.
The 45-second version
What are the new hours at Cowroast Lock and the Marsworth Flight?
Where | Open to boats |
Cowroast Lock (lock 46) | 10:00 to 14:00 |
Marsworth Flight (locks 45 to 39) | 10:00 to 14:00, then a final one-hour passage window before the flight closes fully at 15:00 |
Outside those hours Cowroast Lock is secured. The notice doesn't say who may start the flight during its final hour, only that it closes fully at 15:00 "to allow all vessels sufficient time to pass through".
The Trust says water conservation is now a priority. It describes the hours as "a limited daily window for essential boat movements", and asks boaters to "only navigate when absolutely necessary".
Why are the locks restricted?
The Trust gives two reasons. Rainfall has stayed well below average, and water levels in the Tring reservoirs have kept falling as the canal draws on them. And after a long warm spell, blue-green algae has affected two of its main feeder reservoirs, which reduces the water it can use.
It says there is now only enough water to keep levels up across the southern Grand Union.
Water flows downhill through locks, so the Tring summit has to be topped up. The Trust stores water in four summit reservoirs, filled mainly by local springs, and pumps it up to the canal.
Wendover Spring is the biggest single source, and two pumping stations lift more from boreholes in the chalk. We explain how it works in How do canals stay full of water?
How long will the restriction last?
There is no end date. The notice is subject to review on 12 October, which is a check, not a deadline. The Trust says it hopes to reopen the canal as soon as conditions allow, and that this depends on sustained rainfall over several weeks rather than one heavy-rain episode.
We check the notice every morning and update this page when it changes.
What does it mean for the canal as a whole?
Boats passing through Tring. Anyone on the main line has a four-hour window each day at Cowroast Lock, and the Marsworth Flight has a final one-hour passage window after that. Boats arriving after 14:00 should expect the locks to be secured; the notice doesn't say whether a boat arriving after 14:00 may start the flight in its final hour.
The Aylesbury Arm is closed. The Trust closed it to boats from 09:00 on Friday 2 October because of low water, and reviews that on 9 October.
It's wider than Tring. The Trust says more than half of England and all of Wales are in drought. It has suspended its 14-day movement requirement, and asks boaters to share locks where they can and to shut gates and paddles after use.
The towpath. The notice covers boats. Check the Trust's notices for the towpath before you walk the flight.
What does it mean for a day out from Cow Roast Marina?
Our boats start on the Tring summit, between Cowroast Lock to the south and the Marsworth Flight to the north. The notice's location runs from Lock 39 to Lock 46, but its arrangements list only the locks themselves. It sets hours for them, and lists none for the stretch in between.
Day hire is running. The route we recommend uses no locks: three miles north to Bulbourne and the Grand Junction Arms for lunch, then back. If the Marsworth Flight is open when you get there, ask us on the day about going a little further before you turn for home.
For now, we advise against going south through Cowroast Lock. It opens at 10:00 and is secured at 14:00, so a crew would have to pass it after it opens and be back through before it closes, and a full day to Berkhamsted, eight locks each way, doesn't fit.
The Trust asks every boater to "only navigate when absolutely necessary", and says unnecessary movements may bring a full closure closer. Staying on the summit means a day that uses no locks at all.
We confirm every booking by hand from now until the end of March, so if the notice changes before your date, we'll be in touch.
Other planned closures on this stretch this winter
Separate from the drought, the Trust has planned winter repairs nearby, published in its 2026/27 winter works programme.
4 to 29 January 2027: Marsworth locks 40 to 42. Navigation closed for gate repairs.
1 February to 12 March 2027: Locks 51 and 52 (the Trust lists them as Gas 1 and Gas 2). Navigation and towpath closed for repairs.
The Trust says changes to its published works go through a formal change-control process, and the notices are updated when they happen.
Three things worth knowing before you come
Check the notice on the day. Read the Trust's own notice for Cowroast Lock and the Marsworth Flight, or filter its notices page by Grand Union Canal. This one was amended at 8:16am on Monday 5 October, so it can change quickly.
Blue-green algae. The notice says it has affected two of the Trust's feeder reservoirs. It doesn't say it is in the canal. The Trust's own advice is that children are more at risk than adults, and that where warning signs are up, people and dogs should avoid entering the water altogether. Always wash your hands with soap after contact with the water. If you see it, you can report it to the Trust, and its algae page explains what to look for.
Check lunch plans. The Grand Junction Arms at Bulbourne is the usual stop. Check its opening times before you set off.
Frequently asked questions
Is Cowroast Lock closed?
Not fully. From 2pm on Monday 5 October 2026, Cowroast Lock is open to boats from 10:00 to 14:00 each day and secured outside those hours.
Is the Marsworth Flight closed?
Not fully. The seven locks (45 to 39) are open from 10:00 to 14:00, with a final one-hour passage window before the flight closes fully at 15:00. The Trust says unnecessary movements may bring a full closure closer.
Is it a closure or a restriction?
The Trust's notice is titled a navigation closure, but its type is a navigation restriction, and the Trust amended it from a stoppage to a restriction at 8:16am on 5 October.
Why are the locks restricted?
Rainfall has stayed well below average, and the Tring reservoirs have kept falling as the canal draws on them. Blue-green algae has also affected two feeder reservoirs, which reduces the water the Trust can use.
How long will the restrictions last?
There is no end date. The Trust will review the notice on 12 October, and says reopening depends on sustained rainfall over several weeks.
Can I still hire a narrowboat from Cow Roast Marina?
Yes. Our boats start on the Tring summit, and the northern route to Bulbourne and the Grand Junction Arms uses no locks. For now, we advise against going south through Cowroast Lock. The Trust asks all boaters to "only navigate when absolutely necessary", so please check its notice before you travel.
Is the Aylesbury Arm open?
No. The Trust closed it to boats from 09:00 on Friday 2 October because of low water.
I've already booked. What should I do?
Nothing, unless you'd like to talk it through. Your day goes ahead, heading north. If you have a question, reply to your booking confirmation email and we'll help.
Planning a day on the Tring summit?
Check the Trust's notice first. If you'd like to go ahead, choose a date and book a private narrowboat for up to 10 people. Dogs are welcome and you don't need any experience.
Related: Canal routes from Cow Roast Marina · Your day-hire itinerary from Cow Roast Marina · How do canals stay full of water?
Sources: Canal & River Trust, notice for Lock 46 (Cowroast Lock) to Lock 39 (Marsworth Flight), amended 5 October 2026 · Aylesbury Arm low water levels · notices and stoppages (drought advisory) · Tring (Marsworth) · blue-green algae: what you need to know · winter works programme 2026/27. Map data © OpenStreetMap contributors. Video: lock photo © Stephen McKay, CC BY-SA 2.0.
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