• Lake Hayes is a 280 ha lake (31 m maximum depth), that has become eutrophic due to elevated nutrient inputs from its catchment. 

  • The Lake Hayes catchment has been used for agriculture since late 1800s, but severe degradation was not observed until the late 1960s, when the bottom waters of the lake became anoxic and nutrients previously bound to the lake sediment began to dissolve into the water column. 

  • The acute degradation phase of the late 1960s followed the drainage and conversion of wetlands in the catchment farm land. This land-use change resulted in noticeable discolouration of the main inflow stream for many years. 

  • Catchment nutrient loads have stabilised in the past 20 years, but Lake Hayes remains eutrophic due to its internal phosphorus load. 

  • Commercial development of land including residential subdivisions, ski fields, golf courses, etc in the catchment, continue to increase sediment loadings, threatening the recovery of Lake Hayes.

Lake Hayes catchment - Caruso 2001.png

The Lake Hayes catchment showing the tributary water sampling network used by Caruso (2001). The figure is adapted from Caruso (2001). From the NIWA Land-use impacts on freshwater and marine environments in New Zealand report for the Ministry for the Environment. June 2018.

Since the late 1960’s, Lake Hayes has had severe algal blooms as a result of elevated nutrient loading from the main tributary, Mill Creek, and from nitrate-enriched groundwater springs at the northern end of the lake (Bayer and Schallenberg 2009). From the 1960’s to 2010, the lake was in a degraded state, with blooms of cyanobacteria (blue-green algae), green algae and dinoflagellates occurring intermittently throughout that > 40-year period. After 2006, blooms of the dinoflagellate alga Ceratium hirundinella occurred during most summers. However, Ceratium hirundinella blooms did not occur in two recent summers and the lake maintained a historically high water clarity (Schallenberg and Schallenberg 2017).

Phosphorus (P) loadings during flood events remain high. Nitrate loadings in the creek are above or close to maximum levels with no scope for additional loads.

Importance of the Mill Creek catchment 

ORC (1995) concluded that the Mill Creek catchment is the main source of nutrients to Lake Hayes. Around 80% of the catchment P load to the lake is attached to sediment particles. High historical catchment P loads settled to the lake bottom to become an internal P load, which greatly contributed to the decline and persistence of poor lake health seen over recent decades (Schallenberg and Schallenberg 2017, Gibbs 2018). 

In 1995, the Otago Regional Council developed the Lake Hayes Management Strategy with the stated goal of improving ‘the water quality of Lake Hayes, to achieve a standard suitable for contact recreation year-round and to prevent further algal blooms’ (ORC 1995). The strategy identified issues in the catchment affecting water quality and outlined ambitious actions to be taken to reduce the P load of the catchment, including negotiating with landowners around Mill Creek to establish riparian zones, encouraging the protection and re-establishment of wetlands, and encouraging more sustainable land use in the catchment. This strategy led to decommissioning septic tanks in proximity to Lake Hayes. After this part of the strategy was implemented political impetus was lost and no further action was taken. 

These excerpts are from the NIWA Land-use impacts on freshwater and marine environments in New Zealand report for the Ministry for the Environment. June 2018. (Pg 180 -190)

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Lake Hayes timeline.png

Historical timeline of some key events impacting Lake Hayes. From the NIWA  Land-use impacts on freshwater and marine environments in New Zealand report for the Ministry for the Environment. June 2018.