Lake Okataina

Lake Okataina is one of two Rotorua Lakes classed as “remote”, due to its limited access, native bush and scrubs surrounds and powerboat restrictions.  Most of the inflows to the lake are from subsurface and surface water runoff.  There is no surface outflow but a likely subterranean outflow to Lake Tarawera.

Action Plan Status:  Working party to be initiated
Quality Now:  2.9 TLI
Quality Goal:  2.6 TLI

Lake Okataina's Trophic Level Index (TLI) has fluctuated between 2.6 and 3.1 since 1993.  The TLI is currently above the mid-1990s level.  The key nutrients of phosphorus and nitrogen have both increased significantly, which has resulted in higher phytoplankton (algae) levels.  The lake bed sediments are now also regularly turning anoxic at April, after the lake stratifies the October before.

It is not known why Lake Okataina’s water quality has declined, and whether it is part of a natural lake cycle or a human-induced change.  This uncertainty hinders development of lake management actions.  Further research should identify the factors and lake processes that drive Lake Okataina’s water quality. 

Environment Bay of Plenty has measured and sampled the inflows to Lake Okataina.  A discussion of the results will be posted on this website when available.

• Compare lake level changes to water quality changes, to try and detect any correlation.
• Assess human-induced nutrient sources to the lake: livestock grazing to the south and west of the lake.
• Determine septic tank inputs from the campground and the lodge.
• Consider introducing a ‘Rule 11’-type plan variation to control nitrogen and phosphorus discharges to the lake.
• Monitor nutrient releases from lakebed sediments during autumn.