 As the Wisconsin glacier began its final
retreat, some 11,000 years ago, it left behind a barren, rubble-strewn landscape in the
area of the Grindstone Creek. By the 1600s, the bottom portion of the watershed was a rich
marsh habitat dominated by willows. The area south of the Niagara Escarpment was the
northern limit of the Carolinian forest ecosystem; characterized by sweet chestnut, black
walnut, butternut, flowering dogwood and sassafras. The drier areas were blanketed by
dense forests of red and white oak, hickory, ash, basswood, sugar maple and stands of
majestic white pine.
 The creek teemed
with fish, in particular salmon at the mouth and trout above the escarpment. Large
predators such as bear, cougar and the timber wolf lived in the watershed. The Earliest
French explorers thought the area was "the earthly paradise of Canada". In the
1800s, most of the creek was harnessed to supply power for mills and the creek was
beginning to show signs of exploitation. By 1920, only 10% of the watershed remained
forested and the strong, regular flow of the Grindstone was permanently affected. This was
compounded by the filling and draining of wetlands, sources of water for the creek.
Runoff,
particularly the spring freshet, became more sudden and intense. The flow became less
consistent and more seasonal.
 By the early
twentieth century, fish and wildlife populations showed changes. The fishery was no longer
as rich or diverse. Atlantic salmon were gone and large sturgeon were disappearing. Carp
started to increase in the estuary as water quality in the harbour declined. Some larger
mammals like the timber wolf, cougar and marten disappeared while others like white-tailed
deer and beaver increased. Introduced species such as the European hare, starling and
house finch were now found in the watershed.
The mouth of the creek is known as Valley Inn
named for a hotel that once stood on the site. (north of the Bailey Bridge). The Valley
Inn was built prior to 1830, and prospered until the 1920s when Hwy. #2 was rebuilt and
by-passed the Valley. Until then, Toronto bound traffic from Dundas and points west came
through the Valley Inn area to climb the escarpment on Snake Road.
 The Grindstone Creek estuary was the original
outlet for Cootes Paradise until construction of the Desjardins Canal. The connection
between the Grindstone Creek estuary and Cootes Paradise was lost completely with
construction of Hwy. #403 in 1963. By 1985, only 5.1 ha. of emergent aquatic vegetation
remained in the estuary, a substantial decline from the 37.8 ha. recorded in 1934. In the
1940s the estuary was deeded to Royal Botanical Gardens.
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