Grindstone Marsh Then and Now

By Tys Theijsmeijer, Senior Director of Ecosystem Stewardship Programs and Policy

Grindstone Marsh refers to the marsh at the mouth of Grindstone creek within Royal Botanical Gardens natural areas.  This marsh is about 60 hectares in size, among the largest on Lake Ontario, and forms a 3km long narrow habitat extending upstream into the Hendrie Valley Nature Sanctuary.  It is a diverse environment of floodplains, oxbow ponds, rare species, and crisscrossed by roads, but also with the main area of it unrecognizable as a marsh. This area is located south/downstream of the Valley Inn Trail crossing, sheltered behind the Carrolls Point peninsula in Hamilton Harbour and lacks the plants.

The main part of the marsh remains unrecognizable as it has long lost its normal marsh vegetation leaving it a murky bay and the illusion of depth, losing its last marsh remnants, water lilies, in 2012 during extremely low Lake Ontario water levels. This marsh area is now often referred to as Carrolls Bay in error, losing the separation with the adjacent Carrolls Bay, a deeper sheltered bay immediately behind Carrolls Point, and once fringed by the marsh’s vegetation.  This shallow marsh area becomes only recognizable during the late fall period when water levels seasonally drop, exposing the bottom.

Every now and then you encounter a fantastic historical black and white photo of a landscape that captures the former state of the local environment. This zoomable high-resolution photo of Grindstone Marsh surfaced through an online post from the Toronto Archives, capturing Grindstone Marsh in a fairly healthy state around 1930. This is in contrast to a current June 2025 photo. The historical photo is part of a collection by the late William James Senior, photographer for the Toronto Star. A minor detail: at the time, it was titled “Cootes Paradise, Hamilton,” instead of Grindstone Marsh. The area was historically the boat entrance to Cootes Paradise, but that connection was lost in the 1850s when railway construction filled it in.

The environmental issues that hold back its recovery of Grindstone Marshes plants are two-fold,

• significant inflow of sediment from Grindstone Creek during rainstorms,
• the ongoing large population of Common Carp that is still found in Hamilton Harbour.

Upstream of the Valley Inn Trail crossing, a marsh becomes recognizable as the habitats are protected for the interim by berms of made of Christmas trees and soil.

Full recovery of Grindstone Marsh habitat is a key objective of the Hamilton Harbour Remedial Action Plan. As part of addressing Grindstone Creek watershed erosion issue, Conservation Halton with stakeholders and public input is currently developing an updated watershed management plan. This will also help further guide the recently completed City of Hamilton Watershed Action Plan. The dominant source of of erosion issue is the stormwater runoff from the town of Waterdown.  The carp problem remains as the final challenge, limited by overall murky low oxygen water quality that favours this invasive fish vs our native fish. It will only ultimately be solved by full treatment of sewage and by implementation of urban green infrastructure for the urban runoff. City of Hamilton via Green Venture can provide an individual homeowner with financial grant up to $5000 to support a homeowner green infrastructure project.