The Eramosa River rises near Erin, Ontario, and flows southwest through Rockwood and Eden Mills before entering Guelph, where it meets the Speed River. The Speed then continues into Cambridge and joins the Grand River, which holds Canadian Heritage River designation. The Eramosa itself is part of this Heritage Rivers system and sits within the Grand River Watershed.

The most popular paddling corridor runs from Rockwood southwest to Guelph, covering roughly 10 kilometres and taking approximately 3.5 hours at a leisurely pace. A common put-in is at Eramosa River Park in Guelph, where parking is available and the launch is accessible under the Victoria Road bridge, though paddlers should expect to carry boats roughly 150 metres from the parking area to the water. The Rockwood Conservation Area offers another well-known starting point, where the river passes beneath towering limestone cliffs and alongside glacial potholes carved into 425-million-year-old dolomite. The ruins of the Harris Woollen Mill, which operated from 1867 to 1931, stand near the put-in in that area.

Above Guelph, the Eramosa is narrow and winding, flowing almost entirely through forest with the canopy frequently closing overhead. The bottom is gravel and rock, producing riffles at moderate flow. Overhanging branches and fallen trees can require attention, though serious obstructions are not common on the well-travelled sections. There are portages in Eden Mills and around a weir above Watson Road. Water levels are a significant planning consideration: the river requires a minimum flow of around 2 cm/s for the Rockwood-to-Guelph section, and the stretch from Everton to Rockwood needs at least 4.5 cm/s. During low water, paddlers may find themselves pushing through shallow sections. Flow data is available through the Grand River Conservation Authority website.

Where the Eramosa meets the Speed River in Guelph, the confluence forms a T-shape. A covered bridge crosses the river to the north as part of a recreational trail, and the Boat House restaurant with a patio and ice cream shop is located at the junction, with a small dock available for paddlers to stop. The overall character of the river above Guelph is a quiet, forested paddle well sheltered from wind, while the stretch through Guelph becomes somewhat more urban in character.