Significant rainfall in recent weeks has seen the Selwyn/Waikirikiri River flowing under the State Highway 1 bridge again - a rare sight during the last three years which have been dominated by drought.
Strong currents in the headwaters allowed the river to flow about 30km across the plains.
By the start of last week, more than six billion litres of water had flowed down the river, with around five billion of that seeping through the gravels and into the groundwater system.
Environment Canterbury expects the river to dry up again in the next few weeks but this flow is expected to make it easier for the river to fill up again with smaller rain events in autumn, winter and spring.
ECan says the increased flow is good news for the health of the river and if it leads to the headwaters fully reconnecting with Te Waihora/Lake Ellesmere it could help any eels in the flood flows trying to make their way to the sea.