Most know Brennans Creek as the picturesque little stream flowing through Killaloe, but it's much more than that because it drains the largest water catchment area in the Bonnechere watershed. Its 235.2 sq.kms or 90.8 sq. miles is six times larger than the size of Golden Lake itself.
Brennans Creek's vast. catchment' also represents a vast array of interesting landscapes that adds to the appeal of living in Killaloe. Visual artists have known this for years, members of the Group of Seven such as A.Y. Jackson often visited the area in his latter years..
The catchment's two most noteworthy natural features are the Killaloe Swamp and the Silver Lake Wetland part of which is also designated as a 281 ha Provincial Conservation Reserve.
From The Bonnechere River Watershed Project, RiverWatch Report 2011 (pages 24 and 25 and copied below) the quality of Brennan Cr. water flowing through Killaloe based on Benthic Macro Invertebrate monitoring was considered Fair in 2009, 2010 and Good in 2011.