[2] The dark colour is due to the presence of pollution from farms, sewage and stormwater but it is predominantly from pulp and paper mill effluent.

Since 1998 the colour and light penetration (euphotic depth) have improved in the lower section of the river due to less pollution from the Tasman Mill.

[4] In 2010, local iwi took a case to the High Court to shorten the 25 year water discharge permits issued under the Resource Management Act but the appeal was rejected.

[5]: 500  However it also evacuated 3 km (1.9 mi) downstream from the lake at the terminus of the Pokohu lava flow the amphitheatre of the Tarawera Falls.

[5]: 504  This flood resulted in the raising of the river bed (aggradation), and sedimentation problems to 50 km (31 mi) downstream of the lake.