A koinobori is a calibrated instrument, not a toy. Hang a child's numbered carp on the Harrowgate sounding line and the festival reads every milestone they reach — one tick-stop up the pole.
The festival runs as a vertical day-rail. Each session clips to the sounding line at its hour; the filled tick marks the session in progress when you arrive.
Register a child once. The system assigns the next streamer number on the line and opens a milestone gauge that fills as the year is read in.
Mira Okonkwo-Bell, age 7 — assigned to pole-station 04, north bank. Gauge calibrated to the seven-mark scale.
Fourteen pole-stations run the river from the Mill Steps to the weir. Filled stops are raised and live; open stops are still waiting for their streamers.
Mono rank and height columns, serif names, rows held apart by air. Each row carries a graduated gauge chip; a filled green chip means the year's milestones are all reached.
| Rank | Streamer | Height | Year gauge |
|---|---|---|---|
| 01 | Mira Okonkwo-Bell#1841 · station 04 | 7.2 m | 7 / 7 |
| 02 | Tomás Iriarte#0907 · station 09 | 6.9 m | 6 / 7 |
| 03 | Saanvi Reddy#1204 · station 12 | 6.4 m | 7 / 7 |
| 04 | Jonah Feld#0512 · station 05 | 5.8 m | 4 / 7 |
| 05 | Aiko Tanaka-Pryce#0220 · station 02 | 5.1 m | 5 / 7 |
Every pass is a streamer slip — caret notch, tick-rail, one leading sky mark per line. The riverside grounds are free; passes carry the registry and the finale.
Plumb began as a single rope strung between two lamp-posts on the Harrowgate bank, with one streamer for one child and a chalk mark for every milestone reached. The rope became the idea. Today the sounding line threads the registry, the schedule, the map and the ledger — one continuous ink rule that every part of the festival hangs from.
We keep it grown-up on purpose. No mascots, no balloons, no primary-colour clutter — a calibrated, confident civic event a parent is proud to have built. The carp do the talking; the line keeps them honest.
Run by the Harrowgate Riverside Trust, a volunteer civic body, on the first weekend of May. Free to attend; the registry funds the streamers, the gauges and the lanterns.
At lantern-fall on Sunday the streamers come down for the year and numbered lanterns are set on the water — one for every child, drifting down the river the streamers climbed.