The Scottish Greens have attacked an agreement which allows a power station to continue burning sewage sludge.
Longannet power station burns pellets made from sewage
Almost half of Scotland's sewage waste is converted into pellets and burned at the Longannet power station in Fife.
A court ruling last year said Longannet must be upgraded to the requirements of the EU Waste Incineration Directive.
The deadline was Wednesday. However, government environment body Sepa has agreed it can continue burning while a "longer-term solution is sought".
Scottish Water produces more than 110,000 tonnes of sewage sludge each year, a mixture of domestic and industrial waste.
Much of the waste is spread over both farm land and non-agricultural land.
Almost half is converted to fuel and used in electricity generation at Longannet.
This process is regulated by Sepa (Scottish Environment Protection Agency).
The Scottish Greens said that Scottish Water was unlikely to have a proper strategy to deal with the sewage sludge until at least 2010.
They said the government was completely "unprepared" to deal with the amount of waste being generated.
Green MSP Mark Ruskell said: "The Scottish Executive's hands-off approach to getting a grip on Scotland's sewage disposal problem is unacceptable, we are not only breaking the law but are sleepwalking into an environmental crisis.
"The executive urgently needs a strategy to deal with the vast amounts of sludge that will start backing up soon.
"Disposal out at sea is banned, and there are pollution worries about burning it and spreading it on land. That leaves a huge problem of where to put it."
A Scottish Executive spokeswoman said: "We are aware that the Scottish Environment Protection Agency are currently discussing options with Scottish Water and Scottish Power, with a view to identifying solutions that will allow continued disposal of sewage sludge.
"In addition, Scottish Water is also preparing a revised sludge strategy."
A spokesman for Scottish Power, which operates Longannet power station, said: "We have reached a agreement with the Scottish Environment Protection Agency that co-firing, the burning of sludge, is currently the best practical option for the immediate future while a longer term solution is sought."