September 2026
This September was noticeably wetter than August, with rainfall increasing from 71 mm to 129 mm. One flood event was recorded in September compared with no flood events in August. The previous year, the trap site experienced much higher rainfall (261 mm), with a single flood event.
September 2026 recorded a strong increase in rainbow trout numbers compared with August 2026. Rainbow female counts increased from 142 to 206 (+45%), while rainbow male counts increased from 141 to 183 (+30%). Conversely, brown trout numbers declined considerably, with brown female counts falling from 38 to 8 and no brown males recorded in September compared with 3 in August. The reduction in brown trout spawning activity is to be expected at this time of year.
Rainbow trout size and weight remained largely stable. Average rainbow female length increased slightly from 493 mm to 494 mm, while rainbow male length increased from 489 mm to 490 mm. Average weights also showed little change, increasing from 1.44 kg to 1.46 kg for rainbow females and 1.32 kg to 1.34 kg for rainbow males. Condition factors were generally stable. Rainbow female condition remained unchanged at 43.4, while rainbow male condition improved slightly from 40.6 to 40.9.
Overall, September 2026 saw a substantial increase in rainbow trout migration activity, stable fish condition and size metrics, and wetter environmental conditions than the previous month. Compared to last year rainbow trout numbers were about the same however the fish were slightly smaller and lighter.
Graphs and tables September 2026 (XLXS, 67K)
August 2026
Rainfall was much lower in August (71 mm) than in July (163.5 mm), while no flood events were recorded in either month. The August 2026 figure was more than double the rainfall recorded the same time last year.
Total fish counts increased slightly from 312 in July to 324 in August (+4%). This was driven by increases in rainbow trout, particularly rainbow hens (142 vs 108), while brown trout numbers declined. Average lengths were generally stable, with rainbow trout slightly larger in August, while brown trout lengths showed little change. Average weights were also similar month-to-month, with modest increases for rainbow hens and slight decreases for brown trout. Condition factors improved for brown hens but declined slightly for brown jacks and rainbow trout.
Compared to the previous year, total fish counts increased substantially from 217 in August 2025 to 324 in August 2026 (+49%), with the largest gains occurring in rainbow trout numbers. Average weights were lower for most groups compared to last year, particularly rainbow trout jacks (1.32 kg vs 1.48 kg) and brown males (2.14 kg vs 1.90 kg).
Overall, August 2026 recorded higher fish numbers compared to the previous July 2026 and August 2025, particularly due to strong rainbow trout returns. Fish size and weight remained broadly comparable to July but were generally lower than August 2025, suggesting increased numbers of smaller fish entering the trap.
Graphs and tables August 2026 (XLXS, 67K)
July 2026
Recoded rainfall eased to 164 mm at the site of the Waipa Stream spawning trap in July, with no flood events recorded. Overall fish numbers were down compared to the previous month, where rainfall was much higher.
Brown trout numbers in particular dropped, with 71 fish processed, compared to 157 in June. This is partially due to reduced flows but also reflects historic patters, where brown trout tend to start their migration earlier, peak earlier and drop away earlier. The longest and heaviest brown was a hen of 660 mm and 3.9 kg.
Rainbow numbers were also slightly down. Rangers processed 241 fish, which was a reduction of 40 fish compared to the previous month. The longest rainbow (590 mm) was a hen with a fin-clip scar indicating it was a repeat spawner. The heaviest was a jack that had also spawned previously, which weighed 2.45 kg.
We anticipate higher rainfall and increased flows will trigger further pulses of rainbow trout heading upstream.
Graphs and tables July 2026 (XLXS, 67K)
June 2026
The return of significant rainfall at the site of the Waipa trap prompted a surge in fish numbers, with both brown and rainbows significantly up on the previous month. A total of 438 fish were processed with rainbows now in a clear majority. There was a single flood event.
Fishery Rangers processed 157 brown trout through the trap in June, which is much higher than the 35 trout processed the previous month, and nearly double the numbers recorded during June last year. The longest and heaviest brown was a hen that recorded 690 mm, 4.05 kgs.
Rainbow trout numbers trapped in June also jumped dramatically compared to last month. Only 36 fish were processed in May, compared to 281 recorded in June. The heaviest rainbow was a hen that registered 2.2 kgs, while the longest was another hen of 580 mm.
Data confirms the spawning migrations are in full swing, with large numbers of trout are in the rivers. Fresh fish will regularly enter the rivers and move rapidly upstream during rain events.
Graphs and tables June 2026 (XLXS, 67K)
May 2026
The Waipa Stream fish trap was recommissioned in May, enabling Fishery Rangers to collect data about trout spawning migration patterns. This important work allows consistent data collection across multiple years at this important Tongariro River headwater stream.
Rainfall was very low this year with only 52 mm recorded at the site of the fish trap throughout May. There were no flood events.
Brown trout spawn early but limited rainfall and reduced flow rates likely impacted the numbers reaching this headwater stream. Fishery rangers processed only 35 browns, which is higher than the 23 trapped last year but much lower compared to 80 fish recorded in both 2022 and 2023. Overall, browns averaged 558 mm in length and 2.2 kg in weight. These figures are slightly down on last season and well below the exceptional fish encountered in 2022, where browns averaged 607 mm and 3 kg respectively.
The rainbow trout numbers trapped this year also reflect the reduced flow rates. Only 36 fish were recorded compared to the 71 processed last year. Rainbows averaged 478 mm and 1.23 kg which is slightly below last years figures but significantly down on the solid fish trapped during May 2022 (531 mm and 1.9 kg).
We will continue to publish updates from the Waipa Stream fish trap throughout the winter season.