River & Ponds

Having a river run through the Arboretum as well as several ponds, not only makes for a diverse landscape (ecological diversity), it makes water – essential to the trees, shrubs, grasses and wildlife – readily available.

The East Holland River

The east branch of the Holland River begins its journey through the Lake Simcoe Watershed, at its headwaters to the south of Aurora in the Oak Ridges Moraine, and flows north through the Arboretum from Wellington Street to St. John’s Sideroad. The river continues north until it enters Lake Simcoe at Cook’s Bay.

In the early history of Aurora, this part of the East Holland River was an important source of water for agriculture, irrigation and mill operations. In the 1800s, the river supported a sawmill operation and brewery and prior to this was likely a source of fish and other food for indigenous people..

Today, the river provides habitat for aquatic and terrestrial wildlife. Shrubs commonly found along the banks are dogwood, willow, cedar, alder and elderberry. Plants such as Joe Pye Weed, goldenrod and rushes are also found. The juvenile stage of many insects, including mayflies, stoneflies and caddisflies live under the rocks and on submerged vegetation. They require oxygen-rich, cool running water and are indicators of water quality. Caddisfly larvae are important food sources for brook trout, which we hope will re-establish themselves here as water quality improves. In the summer, water striders are easily spotted, as they appear to skate across the water surface searching for other invertebrates.

Many birds and mammals are found in and around the river. In the spring and summer, Yellow Warblers, Song Sparrows and Alder Flycatchers forage for food and nest among the shrubs lining the stream banks. Muskrat, beaver, even otter and mink, may occasionally be spotted by a quiet visitor, particularly in the early morning or evening.

Water flowing through streams tends to erode the outside of bends and to deposit silt on the inside. This action leads to the typical meandering watercourse seen in southern Ontario. While the actual distance between Wellington Street and St John’s Sideroad is only 2 km, the East Holland River’s total meandering length through the Arboretum is 5.1 km and its elevation drops 7 metres over that distance.

Much of the Aurora Arboretum land occupies the floodplain, the lower flat area adjacent to a watercourse. When the volume of water is too much for the river to accommodate, it will overflow the banks into the floodplain, which temporarily stores the water. If you visit the Arboretum in the early spring or after a particularly heavy rainstorm, you will see the valuable function of the floodplain at work and why it is important not to build in these areas!

The Lake Simcoe Region Conservation Authority (LSRCA) regulates the Holland River and associated floodplain. Floodplain areas around rivers have been protected from development in Ontario since the 1950s, following the damage caused in 1954 by Hurricane Hazel. The ACA works in partnership with LSRCA and the Town of Aurora to protect the stream by planting native trees and shrubs such as cedar, willow, dogwood and nannyberry along its bank.

Riparian (river bank) vegetation serves many important functions. It provides shade to keep the water temperature cool, which is important for fish habitat. The vegetation filters excess nutrients and sediments from runoff before it enters the river. This improves water clarity and helps to stabilize the stream banks. The combined effort of many partners has improved the water quality of the Holland River in recent years.

Stormwater Ponds

The pond off Hollandview Trail is the largest of four Stormwater Management (SWM) Ponds in the Aurora Arboretum and one of the largest in Aurora. SWM Ponds have become common features in the urban landscape as a method for managing stormwater runoff in urban areas. More hard surfaces, for example, roads, driveways, and roofs, mean less rain soaking into soils and more running overland into streams, lakes and wetlands. This is bad for water quality because as the water flows over these hard surfaces it gets contaminated with oils, pesticides, fertilizers and other residues.

There are 6 SWM Ponds in ACA. These ponds were originally designed to manage runoff, but now are also used to help improve water quality in the watershed. When stormwater is temporarily retained in SWM Ponds, sediment settles to the bottom, and vegetation helps filter excess nutrients.

These ponds have become valuable habitats for a variety of native wildlife. Many birds make use of the SWM Ponds and the habitat surrounding them. The Red-winged Blackbird is a common nesting bird in the cattails around the edge. Great Blue Heron, Double-crested Cormorant, Trumpeter Swan and Belted Kingfisher are also regular visitors. Canada Geese and Mallard Ducks moult their flight feathers annually and this pond provides a safe roosting area for them during this flightless stage. Tree and Barn Swallows feed on flying insects over the open water and some nest in the local bird boxes.

Amphibians, reptiles, fish and mammals also inhabit this pond. The distinctive call of the Green Frog, often compared to the twang of a plucked banjo string, can be heard throughout the summer. Snapping Turtles forage out of sight under the water and are rarely seen. When walking around the pond, look for the dome-shaped homes of Muskrat, built out of marsh vegetation among the cattails. This is a protected habitat; fishing or removal of any wildlife is prohibited.

The Farm Pond

Aerial photographs reveal that this farm pond was created between 1954 and 1969 by local farmers to provide a reliable source of water for their farm animals.

This pond is not directly connected with the nearby East Holland River, thus rain and snowmelt are the major water sources. Since it has not been observed to dry up, even during prolonged drought conditions, it is also likely that some groundwater or spring feeds this pond. In contrast, the nearby SWM was built by the Town specifically to deal with runoff from our paved streets and parking lots. Both types of ponds are important to the wildlife of this area.

Although no longer used for farming, this pond now functions as an important habitat for numerous wetland species. Aquatic plants growing under or emerging above the pond’s surface, provide food and shelter for both aquatic and terrestrial wildlife. In summer, most of the surface is covered with Common Floating Pond Weed, with bulrushes and cattails nearer to shore. Growing around the edge of the pond are several grass species, such as reed canary grass and scattered native flowering plants including Blue Vervain, White Turtlehead, Spotted Touch-Me-Not (Jewel-Weed) and Joe Pye Weed. In drier areas, you can find Common Milkweed, an important food source for the Monarch Butterfly during both its adult and larval life stages. Mature trees and shrubs near the pond provide shelter from prevailing winds.

This pond supports large numbers of aquatic creatures including water beetles, water boatmen, mayflies and several species of dragonflies. In spring, this is the best pond in the Arboretum to hear the male American Toads calling to attract females. Toads lay their eggs in long parallel strings on submerged weeds and twigs. Some years, hundreds of tadpoles hatch, feeding mainly on algae as they begin to grow legs. By early July, the tadpoles become very small toadlets that leave the pond, joining the adult toads to forage for insects in the surrounding grassy areas. These amphibians hibernate over winter, buried underground below frost level and return to the pond only to breed. If you live nearby and are lucky, an Aurora Arboretum toad may make its way to your garden or yard. Toads are very beneficial because they are a natural way to keep many insect pests such as slugs under control.

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