After three years of work, the Silver Fern Farms meat co-operative plant at Belfast in Christchurch is no longer discharging its treated waste water into the Waimakariri River.
Instead, the water is piped to Christchurch City Council's treatment plant at Bromley.
The Canterbury earthquakes disrupted construction of the new pipline, which started in 2009.
Silver Fern farms' chief executive, Keith Cooper the pipeline work is part of a wider upgrading programme at Belfast, the company's main South island beef processing site.
Canterbury Regional Council says diverting the waste water discharge will significantly improve water quality in the lower Waimakariri River.
It means fishing and recreational activities can take place at all times except when the river is in flood.
Mr Cooper says the same sort of upgrading process is also going on at other Silver Fern processing sites, as new waste treatment technology becomes available.