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Up the River Blackwater - Osea to Maldon 

Competitors in the Annual Maldon Mud Race

The River Blackwater

The upper reaches of the River Blackwater harbours a secret or two. Whilst there are some great little creeks and and intruguing harbours, there is also an Island that was a top secret naval base and Maldon, which made the area famous for its Sea Salt.

The Blackwater is wide and deep as it runs past Mersea Island and Tolesbury to its North and Bradwell to the South. The river narrows as it approaches Osea Island and the Marconi Sailing Club, which is where our journey starts.

Moorings on the southern edge of the river near Marconi SC.

A shoreline dotted with masts and a series of mooring trots denotes the Southern side of the river as we pass the Stone and then Marconi Sailing Club. A Green lateral mark (No1) to the North indicates the channel leading off Goldhanger Creek.

Marconi Sailing Club and the Marconi red lateral mark (chart point 1)

Osea Island

Deep water passes to the South of Osea Island. A green lateral mark (No3) keeps you clear of the drying bank called ‘The Doctor’ on Osea’s SW side and marks the SW extent of the popular Barnacle anchorage that nestles off Osea’s South East corner. Osea has been inhabited for approximately 5000 years. In more recent times, it was a Victorian alcoholic rehabilitation centre and, rumour has it, local sheep farmers who crossed the tidal causeway had a roaring trade smuggling bottles of ‘medicine’ to patients by hidding the bottles in the fleece.

The Admirallty requisitioned Osea during the 1st World War for use as a top-secret naval base. ‘S.S Osea’, was so secret that many locals had no idea that over 1000 sailors were based there. Today the island is privately owned offering holdiay accommodation.

Barnacle anchorage to the South East of Osea Island (chart point 2)

Lawling Creek

The start of Lawling Creek is opposite to the Southern tip of Osea Island. Red lateral mark (No2) indicates the start of the channel which courses South Westerly towards Blackwater Marina. The Marina was created during the 2nd World War, the government financed the building of a boatyard in Mayland to allow the Cardnell brothers, Tom & George to build much needed Motor Torpedo and Gun Boats.

Distinctive house and remains of the landing pier on the Southern tip of Osea Island (chart point 3)

Back to the Blackwater and Osea Island, as you pass Green lateral mark (No3) the channel turns North West until the Northern bank starts to show itself and moorings start to increase once again. Red lateral mark (No8) indicates a sharp turning point whereby the channel sweeps around to the South West becoming Colliers Reach. The Northern bank is home to Blackwater Sailing Club and the area is very busy at the weekends with dinghy racing.

Blackwater Sailing Club on the Northern Bank as the channel turns SSW into Colliers Reach. (chart point 4)

Heybridge Basin

A couple of cables into Collier Reach brings you to CRS Marine Boatyard which has the odd mooring by arrangement and where the old chandlery has been converted into a tea room managed by Wilkin & Sons of Tiptree who are famous for their jams.

The lock, buildings and traffic signals at Heybridge Basin come clearly into view. The basin is the start of the Chelmer & Blackwater Navigation which is a 13 mile canal connecting Chelmsford to the sea. The project commenced in 1793 and was a main supply artery until it fell into disuse in the 1970’s. It’s trade now are the multitudes of pleasure craft and moororing is available to visiting craft within the basin.

Normally locking out occurs first and when the traffic light is green you can make your approach. Leave the lock approach buoy close to starboard and head towards the withies. Call the lockeeper on Channel 80 for advice.

Entering the lock at Heybridge, the traffic light on green can be seen on the shore to the left of the withies (chart point 5)

The Sea Lock is operated 1 hour before HW to 30 minutes after HW. During the summer months (April to September) the lock operates on all daylight High Waters. Due to it’s popularity during the summer months it it is always advisable to book a berth in the Heybridge Basin, especially at weekends when yacht club rallies often visit the Basin.

The Heybridge lock & basin.


Passing Heybridge, Colliers Reach continues to the South South West, turning to the North West and hugging the Northern Bank. The channel continues to hug the Northern bank until you are roughly North of the Maldon Pier head, near the Maldon Sailing club, at which point the channel crosses to the Southern bank and stays there all the way to Maldon.

Pier head at Maldon (chart point 6)

The first settlers to the district came in the Bronze Age and settled to the north of what is now the town of Maldon. Salt marshes proved popular for salt harvesting as shown in the 1086 Doomsday survey where 46 salt pans were recorded in the Maldon area.

Hythe Quay at Maldon takes it’s name from the Saxon word Hythe meaning landing place and typically a multitude of Sailing Barges are seen moored up. Maldon sailing barges traded up and down the east coast and supplied much of London with agricultural products. Today, it’s a barge and traditional boat mecca and many barges still trade but now mainly with human cargo - for charter and river trips.

It is best to contact Maldon tourist Office for availablity on the Quay, but if you are staying you should be capable of taking the ground.

Maldon Quay lined with barges (chart point 7)

Maldon is a popular tourist destination by land and worthy of a visit by sea as long as you keep a keen eye on the tide to avoid becoming stuck in the mud of which there is plenty. So much in fact that Maldon now hosts an annual fundraising mud race with competitors running through the mud from Maldon across the other side of the river and back again.

Fact file

Tollesbury Marina
Bradwell Marina
Blackwater Marina
Goldhanger Sailing Club
Marconi Sailing Club
Blackwater Sailing Club

Tollesbury Marina
Ch 80 or 37 phone 01621 869202
Bradwell Marina
Ch 80 or 37 phone 01621 776235
Blackwater Marina Ch 37 phone 01621 740264
Heybridge Basin Ch 80 phone 01621 853506
CRS Marine Phone 01621 854684
Hythe Quay
(Maldon Tourist office)
Phone 01621 856503


Walton on the Naze
3.8m MHWS 4.2
MLWS 0.4
Neap 2.3m MHWN 3.4
MLWN 1.1

Osea Island   Range Heights
Spring 4.9m MHWS 5.3
MLWS 0.4
Neap 3.1m MHWN 4.3 MLWN 1.2

Maldon Range Heights
MHWS 2.9
MLWS dries
MHWN 2.3 MLWN dries


Barnacle Anchorage South East corner of Osea Island
Avoid anchoring on the Oyster beds


Imray Y17
Admiralty SC5607


Chart Y17 is reproduced with the kind permission of Imray.

Chart copyright UKHO.

Words & pictures By Simon & Vicky Jinks, SeaRegs
©SeaRegs 2012

© Crown Copyright and/or database rights. Reproduced by permission of the Controller of Her Majesty’s Stationery Office and the UK Hydrographic Office (

This material is not for resale, redistribution or copying.
Not to be used for navigation.

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