The size of David Farley's win in Saturday's Farrer by-election sits in the booth-by-booth detail. One Nation's primary vote surged to historically large margins in the irrigation towns of Griffith, Leeton and Narrandera — the agricultural heart of the southern Riverina — as Liberal candidate Kate McBride saw her support hollowed out across rural polling places.

Griffith, the regional centre, recorded a One Nation primary above 45 per cent in several booths, with the Liberal vote falling below 30 per cent in places where the Coalition has historically polled in the high 50s. Leeton and Narrandera produced similar swings; the smaller villages around Hay leant even further toward Farley.

Local figures pointed to two issues at the door. The Murray-Darling Basin Plan and ongoing water buybacks are blamed across irrigator country for shrinking farm cash flow; Griffith mayor Doug Curran said in an interview Sunday that "every grower I've spoken to says water reform is the first conversation they have with anybody on a ballot".

The second issue was the cost of living, particularly fuel and grocery prices in towns whose distances from Sydney and Melbourne make any inflation print bite harder than the national average. ABS data show regional NSW headline inflation running roughly half a percentage point above the metropolitan average for most of the past year.

Independent candidate Michelle Milthorpe, the Climate-200-backed contender, performed strongest in Albury and along the Murray, where higher-income towns gave her primary vote into the high 30s. But she could not match Farley's spread across the irrigation district.

Local National Party officials in the seat have begun urgent post-mortems. The Coalition's preference flow to One Nation in some booths — a second-preference rate above 70 per cent — is expected to be the focus of internal recriminations. Party officials in Sydney are also reviewing how to handle similar contests in neighbouring seats.

The Riverina has a long memory of protest votes; Pauline Hanson herself addressed crowds in Griffith in 1998. What is different this time, local commentators noted, is that One Nation has now produced a sitting MP rather than a Senate-only presence, and intends to organise the seat for the next general election.