Streams and Ponds
PEI streams are small and shallow. On PEI we refer to many streams as rivers, but none are actually large enough to be a true river. They vary in width from 5 cm to 10 m (2 inches to 33 feet) and in depth from 5 cm to 2 m (2 inches to 6.5 feet). 'Rivers' that are wider or deeper than this are estuaries. Most streams are less than 16 km (10 miles) in length.
A typical Island stream begins as a spring. Groundwater flows upward through fractured bedrock and begins to flow downstream in a defined streambed. As it makes its way to the ocean, the groundwater mixes with run-off water from the land. Eventually, stream waters mix with salt water to become an estuary.
The portion of a stream's flow that comes from groundwater is called 'base flow'. On an annual basis, about 60 to 70% of the water in Island streams comes from groundwater. The rest comes from rainfall or from surface runoff. During dry periods, PEI's streams are nearly 100% groundwater.
PEI streams are generally considered to be 'cold'. Groundwater sources (springs or seeps) range in temperature between 8 - 10 degrees Celsius. Only in cases where large, man-made ponds or beaver ponds exist, do stream temperatures become warmer.
Ponds are common along Island streams. Over the last two centuries, most streams were dammed at one time or another to serve industry (grist, lumber, or power mills). Over time, many of these historic mill sites were re-developed. These man-made ponds (there are over 600) are important for recreation and our cultural heritage, as well as for aesthetics and wildlife enhancement. Ponds can also be considered to be wetlands.
With the exception of beaver and barrier beach (or barachois) ponds, there are few truly natural ponds on PEI. Barrier beach ponds are most common along PEI's northern shoreline. Here, continually shifting sands partially restrict stream flow. Water backs up and a pond is formed. These ponds are constantly in a state of change. Sometimes they contain a mixture of fresh and saltwater, although usually they are fresh. Unlike estuaries, barrier beach ponds do not always have an opening through which salt water can travel.