Diving in the Leeds Liverpool Canal can be like entering a "flooded skip" according to the police squad whose officers are tasked with searching its waters.
The Underwater Search and Marine Unit hunts through Merseyside's waters for guns, knives and bullets - often retrieving crucial evidence criminals hoped would never be found.
From the Mersey to Liverpool's park lakes, its divers also play a key role in searching for missing people and encouraging children to be safe around water.
Officers from the Search and Marine Unit often catch the attention of passers-by when they are at work - their equipment and diving outfits making potential crime scenes appear even more dramatic.
Just last month they could be seen working in a lake in Walton Hall Park, where they found shotgun cartridges after a fisherman pulled out an ammunition clip.
While the unit covers the whole of the North West they are often seen on Merseyside and have been drafted in to work on several murder investigations in recent years.
Last year divers could be seen searching bodies of water in Everton Park in connection with the James Taylor shooting probe, while the unit spent months operating from the Sandhills Lane bridge as they examined the Leeds Liverpool Canal following the murder of Lewis Dunne
Searching the canal can be difficult, with efforts based largely on touch rather than sight.
Sergeant Anthony Darbyshire explained: "In the urban sections it’s like diving in a flooded skip, with bicycles, shopping trolleys, motorbikes and any other rubbish lying on the bottom.
"Our task is to feel our way in and amongst the junk to find what we’re looking for.
"On the contrary, the rural sections are quite nice and usually quite clean and can be enjoyable on a sunny day.
"It’s grim in winter whatever the conditions of the canal as it doesn’t take long for our fingers to get really cold and once the feeling is gone there’s no point searching."
Divers typically search the canal by placing a weighted rope across the width of the bottom.
They then use the rope as a guide while they conduct a finger-tip search of the bottom.
Although instinct plays a major role, they often find important items such as weapons and, in the Walton Hall Park case last month, cartridges.
On that occasion the unit's attention was drawn to the lake by magnet fishermen - whose growing number are leading to more and more potentially criminal items being discovered.
Just this week two knives were pulled from a fishing lake during a search in the Northwood area of Kirkby. There has also been a rise in the discovery of mobile phones since the shadowy communications network EncroChat was hacked by investigators last year.
Sgt Darbyshire said there was a "fantastic" feeling when a dive was successful.
He said: "Whether on land or in the water all searchers know the excitement of finding what you’re looking for."
The unit's search efforts extend beyond lakes and canals to the Mersey - on which they also play a security role during major events such as when Cunard's Three Queens cruise ships visited Liverpool in 2015.
One of the most heartbreaking aspects of the North West Underwater Search and Marine Unit's role is the search for missing people.
The squad uses technology such as sonar to search larger expanses of water.
Search and rescue operations were among the most important but most difficult parts of the job, Sgt Darbyshire said.
He explained: "On missing person searches things are obviously different and whilst we may have completed our task the mood is more sombre with the obvious and tragic loss of life.
"The most important part is returning a loved one to a family to hopefully assist with some kind of closure.
"Sometimes we aren’t able to find a missing person and its hugely frustrating for us as we know there’s a family left wondering."
While the police divers play important roles in criminal investigations they also spend a lot of time teaching water safety lessons to children across the region.
Just this week they have been involved in the Drowning Prevention and Water Safety Week.
You can access key water safety advice here.
And you can follow the Underwater Search and Rescue Unit on Twitter, here.
