An ecologist wants the Ministry for the Environment to admit that it has been misleading the public over the quality of the country's rivers.

In an email, the ministry says it will switch from using the phrase 'stable' to 'no evidence of a trend' in future reports.

The phrase 'stable' is often used by government agencies, councils and politicians when talking about the quality of rivers.

Massey University ecologist Mike Joy and other scientists have been telling the ministry that the word is giving the public false hope that rivers are improving.

"I think if you ask the average New Zealander, they would say stable means like someone's in hospital and they're stable - they're not getting any worse, probably they're going to get better, so we can stop worrying. That is not the same as not significant," Dr Joy told Radio New Zealand's Nine to Noon programme.

Late last month, the ministry emailed Dr Joy to tell him of the future change in phrasing.

In a statement, the ministry told Radio New Zealand there have been no statistically significant trends in monitored rivers in the past 10 years, and it believes a lay person would consider that stable.