The scenic waterways of the Spreewald eastern German natural area could remained choked with iron sludge from lignite coal mining for decades, Greenpeace says.

The environmental group, which is leading a campaign to halt an expansion of lignite mining in the German state of Brandenburg by the Swedish energy company Vattenfall, said Thursday its measurements of iron content in the Spreewald waterways taken after extensive June flooding shows iron content is growing despite recent efforts by the state government to control it.

The intricate network of waterways, recognized by the United Nations Educational, Scientific and Cultural Organization as a Biosphere Reserve, is a haven for storks, otters and dragonflies, and for many centuries has been used by its traditional Slavic inhabitants for small farmsteads.

But in recent years the waterways have been discolored by reddish-brown sludge rising from former East German lignite mines abandoned in the Lausitz region decades ago, and since massive flooding in June have been clogged by mud.

In January, the Brandenburg state Parliament unanimously approved a plan to combat the rusty discoloration of the River Spree, saying it would work with the neighboring state of Saxony to put a high priority on the protection of the Spreewald watercourses.

The measures include the re-commissioning and construction of pit water purification systems and new management of a dam at Spremberg. A network of measurement points were created while a commitment to implement new guidelines for dredging sludge were also approved, Radio Berlin reported.

But Greenpeace energy expert Niklas Schinerl told Rundfunk Berlin Brandenburg Thursday the measures haven't been enough stem the tide of iron oxide rising into the Spreewald system.

"A whole ecosystem is choked with mud," Schinerl said, adding that Vattenfall's plans to open five new lignite mines in Brandenburg's Lausitz region will only compound the problem and must be stopped to preserve the Spreewald, located 60 miles southeast of Berlin.

Schinerl said Greenpeace's July measurements showed iron oxide content in the water to be more than 100 milligrams per liter -- 3 milligrams per liter are considered harmful to the environment.

"If the lignite mining continues as planned, the iron sludge will endanger the Spreewald and other waters for around 100 to 150 years," he said.

Vattenfall, moving to meet rising electricity demand in Germany, has announced plans to develop brown lignite coal strip mines in Lausitz, beginning with the Welzow-Sud II mine. The company is intending to mine 204 million tons of brown coal at the site through 2050.

The company in January announced its German lignite mines had increased their output in 2012 to the highest level since 1993 at 62.4 million metric tons, while lignite-fired power output reached its highest level since the end of communism in East Germany at 55 terrawatt-hours, Platt's reported.

The Brandenburg Ministry of Economy supports the Vattenfall expansion and last week dispute's Greenpeace's findings of rising iron content in the Spreewald waterways.

A spokesman for Ralf Christoffer, Brandenburg's minister for economic and European affairs, told Rundfunk Berlin-Brandenburg the environmental group's measurements were off-base.

"A host of measures" have been taken, he said, adding that some areas of the Spreewald had been cleared of mud and discoloration while the average value of iron loading was less than 1 milligram per liter.