More than a third of patients in critical care in Wales have Covid.
A doctor working on the front line has said that operating at that capacity will lead to a fall in standards.
Speaking on the BBC Politics Wales programme, intensive care consultant Dr Jack Parry-Jones said more than 35% of patients in critical care currently have Covid.
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While he said that at the worst stage of the first wave it was 90%, staff are currently under "enormous pressure" and "standards of care will fall".
"Every week, our baseline critical care capacity in Wales is 152 beds, which is the fewest per head of the population in the UK.
"We're currently running at 123% capacity and of those over 35% of them have been taken out with patients with Coronavirus infection."
Wales' seven-day coronavirus infection rate has now reached the highest level since the pandemic began, it has been revealed.
There were also 3,296 new positive cases recorded in today's update, bringing the total number since the pandemic began to 415,829.
Dr Parry-Jones said: "The difficulty with Covid is the time it takes people to get better. So a quarter of patients with Coronavirus will take over 30 days before they get better, so that's the survivors. Those people that die in critical care with Covid those patients whilst we're trying to save them, they still take a significant period of time in critical care.
"So our staff are under an enormous amount of pressure running at that kind of capacity.
"When you're running it that kind of capacity, standards of care will fall and we really struggle across the critical care sector with staffing and that's mainly or particularly nurse staffing, but actually all staffing is extremely difficult".
Asked if critical care was reaching its limit, Dr Parry Jones said: "We can we can flex up. So at the worst stage in the first wave, over 90% of patients in critical care had COVID we had over 200 patients across Wales.
"We can do it, but the problem is standards fall and it's very very difficult for staff and we, it's extremely difficult to retain staff when they're exhausted so they will leave the service.
"At the moment 36% of the baseline of critical care is patients with Covid, so we really, really, need to reduce infection rates.
"Vaccination is incredibly important in doing that, but it's also each individual's responsibility to reduce their risk of getting Covid and to reduce transmission. There's a responsibility on all of us to do that but the vaccination remains the key for us.
"Unfortunately for critical care nothing is going to change, it can only get worse, for at least a month, because it takes that long for people with infection to become critically ill and so whatever happens now we're looking at a minimum of a month to two months with this kind of rate of Covid cases in Welsh critical care.
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