Craig Jackson, a fire officer from Shifnal and James Sutherland, a water safety officer from Claverley, started their four-day jaunt on Friday, June 17.
And the pair are raising funds and awareness for two charities close to their hearts – Seaful and Severn Area Rescue.
On day one, they paddleboarded from Crewgreen on the Shropshire Powys border to Atcham.
Then on the second day of their trip, they completed an impressive 68km stretch from Atcham to Stourport, and on day three they travelled 58km from Stourport to Gloucester.
The last stage of their journey saw them leave Gloucester and paddleboard 52km to their final destination, the Severn Estuary – which they were due to arrive at last night.
Craig said day three had been particularly challenging coming on the back of extreme weather conditions – severe heat on Friday and heavy rain on Saturday – but he explained being on their paddleboards makes them "feel alive".
He said: "Day three was a real grueller, we really felt it.
"We had 11 hours on the board, and when we got up in the morning and we were just in bits.
"We have put so much in over the last few days, and it just really hit us hard, it was longer than we expected, and the river gets a lot slower as we go further down so we have to earn every stroke.
"We were close to tears this morning.
"But being back on the water is great for our mental wellbeing, and when you are in this environment you cannot help but feel alive."
And after four days of camping alongside the river and living out of dry bags, Craig is looking forward to a hot shower and collapsing into bed.
They have currently raised £940 of their £1,000 target for their chosen charities.
Craig is an ambassador for Seaful, founded in 2020, which dedicates its time to connecting people to the ocean and other waterways. James is a volunteer for Severn Area Rescue Association (SARA) which locate and rescue vulnerable people along the River Severn.
To donate: justgiving.com/team/sup-shropshire