Lake Rotoroa (Hamilton)
General information
Lake Rotoroa is a small urban peat lake, formed by a peat dam on top of a levee of the ancestral Waikato River (Green and Lowe, in Clayton and de Winton, eds., 1994). Its catchment comprises parkland and residential housing. The lake is phytoplankton dominated following the collapse of Egeria densa beds in 1989-90. Following this collapse the lake’s Trophic state initially improved as nutrients from the decay of the weed beds left the system but it is now in a stable phyto-plankton dominated state with some recovery of charophyte beds which is probably limited by coarse fish browsing and disturbance (de Winton, Safi, Taumoepeau and Burns, 2006). Egeria densa has also returned to some areas of the lake and is the subject of monitoring and control.
Lake Rotoroa photo by Wendy Paul
Restoration Action
Restoration actions have included the eradication of the exotic Iris pseudacorus (formerly the dominant lake margin vegetation) and its progressive replacement with characteristic native vegetation; the monitoring and control through herbicide application of Egeria densa; the re-introduction of Hyridella menziesi (freshwater mussels, or kakahi); passing stormwater from new developments through vegetation before allowing it to enter the lake; and improvements to edge treatments to minimise mobilisation of sediment into the lake.
Lake Rotoroa Statistics
Area |
54 ha |
Catchment area |
138 ha |
Maximum depth |
6 m |
Mean depth |
2.4 m |
Volume |
1.3 x 106 m-3 |
Altitude |
37 m a.s.l. |
Residence time |
~2 years |
Trophic state |
Eutrophic (TLI 4.76 +- .08, 2006) |
Catchment |
Residential and parkland |
Recreation |
Yachting, model boats, Dragon boating, canoeing etc. |
Restoration progress |
Marginal pest plant eradication and replacement, level management, water quality monitoring and Egeria densa control, attempted nutrient input management. |
Peat influence |
Moderate, lightly peat stained |
Reserve status |
Owned and managed by Hamilton City Council subject to Reserves Act 1977 |
Submerged vegetation |
Nitella sp. aff.cristata, Chara australis beds cover c. 21% of lake area. Isolated beds of Egeria densa. |
Harmful algae |
Anabaena planktonica, Microcystis aeruginosa, Microcystis flos-aquae, |
Invasive fish |
Catfish, rudd, perch, tench, goldfish and gambusia. |
Images
References
De Winton, M.D., Safi, K., Taumoepeau, A., Burns, N. (2006). Lake Rotoroa Monitoring: 2005/06. NIWA Client Report HAM2006-080, National Institute of Water and Atmospheric Research, Hamilton, 2006-11-03.
Clayton, J.S., de Winton, M.D. (eds) (1994). Lake Rotoroa: Change in an Urban Lake. NIWA Ecosystems Publication No. 9, February 1994.
