1. In 1989 a 1.3 km channelized reach of the River Gelså was restored to a new 1.9 km meandering course. The restored reach was subsequently (1989–95) monitored for changes in physical and biological features compared with an upstream channelized reach. Weed clearance and other types of maintenance practices have not been undertaken in either reach since 1990.
2. By 1993 the restored reach had already stabilized, both physically and with respect to diversity and density of the macroinvertebrate community.
3. The upstream reach gradually improved physically during the study period, but remained less heterogeneous than the restored reach, with only a very limited amount of stony substrate. Stone-dwelling macroinvertebrate species were consequently still scarce in 1995, while overall diversity and density of the macroinvertebrate community was similar to that in the restored reach.
4. The results indicate that natural rehabilitation of physical features is a rather fast process, but in some ways cannot match the almost instantaneous heterogeneity obtained by active restoration measures. © 1998 John Wiley & Sons, Ltd.