"Now we know what out to look for," she said.
The original parkrun was set up by then-unemployed Paul Sinton-Hewitt CBE in Teddington, England, in 2004 and has since grown to three million-plus participants in more than 20 counties.
Due to the pandemic, New Zealand is the only country in the world running the event at present, with Whanganui being the 30th event set up around New Zealand.
The 5km course starts downstream from the Cobham Bridge, then heads into town before looping back to the start/finish line.
"It's flat, hard surfaces like concrete or boardwalk," Mellsop said.
The organisers have had messages from people as far as afield as Auckland saying they are coming to the first event.
"People really get into parkrun and they go all round the country doing them and there are people that want to be in the first one here.
"People want to keep the record of doing all the parkruns around New Zealand."
The runs will only be cancelled for extreme weather, Mellsop said.
The run will be launched opposite 282 Taupo Quay on Saturday, July 4, with the briefing starting at 7.50am.
The whole event is run by volunteers and Mellsop said they are essential.
"Anyone interested can sign up online."
The event is free to join in. All contestants have to do is register at www.parkrun.co.nz/whanganuiriverbank before their first run.