The popular spot in Port Meadow, a large park in the city, is the second river in England to be granted this.
It comes amid concern over poor quality of waterways in England, and what this could mean for wild swimmers.
MPs warned earlier this year many rivers containted a “chemical cocktail of pollution” of sewage, farm waste and plastic which could pose a public health risk.
The move by the Environment Agency will give added protections to the sites in Oxford and the Isle of Wight, both popular swimming spots, for those wishing to use them.
It will mean officials will regularly take samples to assess water quality and whether action is needed to cut bacteria levels.
This will begin from 15 May, the beginning of bathing water season.
The new bathing water status followed a consultation. Rebecca Pow, the environment minister, said: “The residents of Oxford and the Isle of Wight have shown their overwhelming approval for these sites as places to enjoy and connect with nature.”
She added: “While bathing water quality has improved in recent years and England now has the cleanest bathing waters since records began, we know that water quality at these sites won’t change overnight. It will take time and all those with a role to play must commit to achieve the necessary improvements.”
At the end of last month, the government released proposals to tackle how often raw sewage is pumped into England’s rivers and lakes – a legal process to prevent the sewerage network from becoming overwhelmed during heavy rainfall – to protect water quality. These included strict limits on when overflow systems can be used.
The plans were announced on the same day official figures revealed water companies discharged raw sewage into England’s rivers, estuaries and seas around 1,000 times a day during the last year, sparking warnings over the impact on public health and wildlife.
The government said an increase in extreme weather events – including heavy rainfall driven by the climate crisis – and a growing population were both increasing pressure on the sewerage system, which was leading to discharges of untreated sewage happening more often than was acceptable.
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