An experienced hiker has called for safety measures after he sank to his waist in what he likened to "quicksand" during a visit to a reservoir.
Sam Rolnick was with his young son at Aldenham Reservoir over the weekend when he says he began sinking in mud.
He described the experience as "terrifying" and wants to warn others of the hidden danger.
He said: "I was with my son who loves nature. We saw some fisherman and while my son was talking to one of them, I’ve gone round the back of the bivvy (tent) and landed in what’s turned into an extremely deep mud pile.
"It can be described as quicksand, absolutely, and it was a terrifying experience because I reacted quickly by falling forward flat and crawling out of the hole."
Mr Rolnick said he last visited the reservoir around seven years ago and had been unaware of the recent history.
The private owners of Aldenham Reservoir, Liberty Lake Leisure, have been draining the water for more than a year because they say it helps ease pressure on a dam wall that is in need of repairs.
The drainage has dramatically changed the reservoir’s surroundings and even forced Aldenham Sailing Club to move on after more than 80 years.
Related: Aldenham Sailing Club officially depart Aldenham Reservoir
Mr Rolnick invited us down to take a look at where he began sinking on the morning of July 3.
His hand and footprints were still visible and he demonstrated with a long stick just how soft the mud is. He also showed a photo where his bottom half was covered in mud.
The mud in question is away from the public footpaths, to the left of the jetty, but it is still publicly accessible. Formerly the land was water.
Mr Rolnick, who was at the reservoir preparing for a 700 mile charitable walk he is embarking on with his son, Jacob, in aid of Mind, said: "This is extremely hazardous. I’m lucky I have a lot of experience with walking and hiking and adventure but this was one of those dangerous moments for me.
"I was unaware of the history, I only just recently moved back to the area. I learned afterwards on social media about some previous incidents.
"There needs to be adequate signage and fencing off and public awareness about this. I don’t want people to go through the same."
There are some signposts which warn of a "deep slurry" but nothing where Mr Rolnick began sinking.
Meanwhile, Hertsmere Borough Council has put up notices warning that high concentrations of blue green algal scum have been found in the reservoir.
The notice says the scum can cause serious health effects and warned that pets and children in particular should be kept away from the water.
Elsewhere, there are signs of public unhappiness with the reservoir owners.
Stickers have been placed on signs which state 'F*** Liberty Lake Leisure', 'Footpath and lake is owned by the public', 'this land is our land', and 'all power to the people’'.
Last summer, around 200 people concerned about the state of the reservoir and its future took part in a protest at the site.
Related: Protest takes place at Aldenham Reservoir in Elstree
Co-owner Mahesh Gosrani has been approached about the incident involving Mr Rolnick as well as the stickers.
Related: Private owners say Aldenham Reservoir is not for sale
Support the Rolnick’s 700 mile walk for mental health charity Mind from Brighton to Dunnet Head in Scotland via their Just Giving page.
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