A flash in the pan?

One of the features of the upper end of the Trent and Mersey canals are the "flashes".  Sometimes they have occurred right beside the canal making a large area of open water.  This shot is Croxton Flash.  The flashes look very tempting but boaters beware, they are invariably very shallow and should you stray into them you will almost certainly get stuck.

The flashes are caused by subsidence as a result of salt mining.  Once on the River Weaver we stopped to top up the water tank and asked the boat already there if they would be long.  The reply was basically "we don't know".  They had gone into the flash (beyond the clearly marked limit of navigation ) and got stuck.  They called the hire company and Canal and River rescue.  Both said there is nothing we can do as we can't get to you without being stuck ourselves.  The only suggestion which they could make was "pump out all the water and dispose of as much extra weight as possible".   Fortunately they had managed to get off after doing this.  They had then been filling their water tank for an hour when we arrived.