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Since 2014 the regional council has taken monthly samples from rivers.
It released information this week which highlighted the levels of slime algae or periphyton in Southland rivers.
According to Environment Southland's figures, none of the 30 sites tested at 27 different rivers and streams fall below the national bottom line for periphyton.
A national bottom line is a level that has been set by the Government.
Environment Southland's director of science and information Graham Sevicke-Jones said it was good news for the region.
"The data we have been collecting monthly shows us that the state of slime algae is better than we thought it was,'' Mr Graham said.