Non-native 'killer shrimp' and zebra mussels are "invading Britain" at a rate never seen before, a government watchdog says.
Higher numbers of complaints about breathing difficulties are thought to have been brought on by record pollution levels in recent days.
Air pollution in the east of England reached the top of the scale as a 'perfect storm' of conditions blanketed parts of the country.
Environmental campaigners have urged politicians not to ignore the cloud of smog that has smothered parts of the UK over the last few days, saying they are "playing with people's lives".
Friends of the Earth's Jane Thomas told Daybreak, "29,000 people a year die prematurely in London alone" from pollution created by emissions.
Air pollution levels remain high across parts of England and Wales but are expected to reduce later today.
The Department for Environment, Food and Rural Affairs (Defra) reports that more than 20 areas from northern England down to the South East are still gripped by high levels of pollution this morning.
But a fresh air mass arriving later is expected to push the pollution eastwards over the North Sea, weather forecasters have said.
Pollution levels remain 'high' across England and south Wales and 'very high' in London, the Department for Environment, Food and Rural Affairs (Defra) has said.
Showery outbreaks of rain will persist overnight across northern England and much of Scotland.
Misty and murky conditions will be forming out toward the North Sea coast, and we are still pulling up that polluted air from the south-east.
Things will be changing overnight, however - a south-westerly air flow will feed in much cleaner, fresher air.
The number of 999 calls from north-west patients struggling with breathing problems has soared by 15% this week, the region's ambulance has said.
According to the Manchester Evening News, the North West Ambulance Service has seen 985 such calls between Sunday and Wednesday compared to 858 between in the previous four days.
A spokeswoman for the service told the newspaper that while the increase appeared to be linked to an increase in pollution levels, the cause was not completely certain.
West Midlands Ambulance Service has experienced a noticeable spike in call-outs linked to breathing problems and chest pains.
Daily figures for calls reporting breathing or chest problems were largely level at around 460 on Friday, Saturday and Sunday last week.
But the corresponding figures for the first three days of this week were 547, 510 and 501.
The service covers Shropshire, Staffordshire, Warwickshire, Herefordshire and Worcestershire.
Pollution levels have eased slightly in the south-east but have now increased in the West Midlands, north-west and Merseyside, according to the Department for Environment, Food and Rural Affairs (Defra).
High pollution now in the West Midlands, North West & Merseyside. Improvement from V High to High in the South East. http://t.co/BA1M8OK7C9
Defra have issued health advice for at-risk individuals as 'very high' pollution levels hit London.
London Ambulance Service revealed earlier that there had been a 14 per cent rise in the number of people calling 999 for help with breathing difficulties.