The RIM Park lands encompass two main ecological areas. 

1. East RIM Park Floodplains, including:
   the Horst Floodplain, on which are the Horst Tributary and Grand River Corridor Buffer
   the Martin Floodplain
   the Rural East Woodland/Wetland
2. West RIM Park, an upland system, including:
   Critter Creek
   the Cedar Esker and Kame
   Eastbridge Woodlot

A floodplain is built by a river as it erodes sediment from upstream locations and deposits it downstream. In creating the floodplain at RIM Park, the Grand River has at some point occupied every part of the valley.

Floodplains are constantly disturbed ecosystems, subject to erosion, deposition of sediments during late winter or spring flooding, and damage to vegetation caused by blocks of ice. Floodplain plants must be adapted to surviving their unstable environment.

However, because floodplains are regularly disturbed, they also provide ideal habitat for weedy, invasive non-native species. This, along with their historical use as choice settlement areas, makes intact native floodplain communities a vanishing and valued ecosystem. Some remains of the original floodplain forest can be found in RIM Park as small groves and scattered individual trees such as willows, bitternut hickories and black maples.

RIM Park is unique in providing one of the longest stretches of public access to the Grand River shoreline. In planning the park, City of Waterloo staff strive to balance use of the land by our citizens, with recognition of the sensitivity of the watershed area and the historical significance of the lands.