The Grey — Māwheranui — gathers the rain of the Southern Alps and the Paparoa Range and runs broad and powerful through the Grey valley to the sea at Greymouth, a big West Coast river of long runs and bush-lined reaches. Strong brown trout hold its runs and the clearer tributaries, in high-rainfall country where the river rises and falls fast.

Wading: Big spate river, fast rises after rain, slick gravel — read the level

Practical guides describe green beetles in early summer giving way to cicadas from late summer on the fishable middle and upper reaches — broad seasonal guidance from secondary sources, not measured insect counts.