Freshwater ponds

Sable Island National Park Reserve

Freshwater ponds can be found on Sable Island, despite the island's remote location in the Atlantic Ocean.

Five horses following each other next to the edge of the pond.
A freshwater pond at Sable Island National Park Reserve.

Freshwater

Sable Island receives all of its fresh water from either rain or fog.

Due to the sandy nature of the island, all rainfall seeps directly into the ground. Sable Island’s infiltration capacity (capacity of the ground to absorb water) far exceeds the heaviest rainfall observed on Sable Island, so there are no streams or other running water on the island.

Freshwater lens

Rainfall collects below the island’s surface and forms a freshwater lens. As freshwater is less dense than saltwater, it floats above it.

A horse drinking from the centre of the pond.
The ponds provide essential habitat for many species on Sable Island.
Two freshwater ponds surrounded by dunes and vegetation.
The ponds are only located in the west end of Sable Island.
An aerial view of a freshwater pond surrounded by green vegetation.
Horse trails lead across the grass covered dunes to a pond.

Freshwater ponds

In low-lying areas, the surface of the freshwater lens is exposed. This exposed freshwater lens forms the freshwater ponds on Sable Island. These ponds are generally surrounded by a barrier of sand in the form of dunes.

Located on the western half of Sable Island, the freshwater ponds provide essential habitat for a large variety of species, including Sable Island’s wild horses.

Water testing

Most ponds in Sable Island NPR are slightly basic (i.e. not acidic) unlike most lakes on the mainland of Nova Scotia.

Water chemistry is tested with a handheld device called a ‘sonde’ that measures parameters such as the acidity (pH) and the amount of oxygen in the water. Other water quality parameters are tested in a laboratory.

Concerns

There are two major concerns about the freshwater ponds on Sable Island: 

  • in-filling of the freshwater ponds by windblown sand
  • mixing of the ocean salt water with the freshwater (salinization)

The lake is a thin sliver of water surrounded by sand next to a long dune.
Lake Wallace photographed by Debbie Brekelmans, Sable Aviation, July 2008.

Lake Wallace

When Sable Island was first encountered by Europeans, it had a huge saltwater lagoon that was open to the ocean. Sailors used this bay to shelter their boats. In later years, with the shifting of sands, the lagoon became closed off from the ocean. In 1777, the saltwater lagoon now named Lake Wallace stretched 22 km across the interior of Sable Island.

Despite its earlier massive size, in 1984, the lake measured only 200 m in length — a 110 times decrease in size! This was a result of in-filling of the lake by blowing sand.

In late 2011, Lake Wallace ceased to exist as a permanent feature. The area still experiences periodic flooding from freshwater (heavy rainfall) or saltwater (from wave overwash at high tide or during a storm).

Sable Island maps: 1767 to 1959

Six maps of Sable Island from 1767 to 1959 show the island shifting east and Lake Wallace shrinking.
Historical maps of Sable Island By M. L. Cameron, January 10, 1963, from the Nova Scotia Archives.
Text version

This series of maps shows the changes in shape and length of Sable Island from 1767 to 1959. It also shows the formation of Lake Wallace and how it changed over time. Lake Wallace did not exist in 1766. Lake Wallace grew smaller between 1851 and 1952. The size and shape of the lake remained the same from 1952 to 1959.

From top to bottom, the maps include: 

1. Sable Island, 1766-67 – J.F.W. Des Barres (After Goldthwait)

2. Sable Island, 1851 – Bayfield and Shortland (After Goldthwait)

3. Sable Island, 1899 – Bayfield, Shortland and Canadian Hydrographic Service (After Goldthwait)

4. Sable Island, 1952 – H.L. Cameron, Air photo survey

5. Sable Island, 1955 – H.L. Cameron, Air photo survey

6. Sable Island, 1959 – H.L. Cameron, Air photo survey


Water holes

A group of horses take turns drinking from a water hole dug in the sand.
On the eastern end of Sable Island, there are no ponds.
A small hole dug in the sand with water.
 The horses dig small water holes in the low lying areas to access the water from the freshwater lens.
Three horses take turns drinking from a water hole in the sand.
Horses take turns drinking from a small water hole.

Additional information

Freedman, B., Lucas, Z. and S. Blaney. 2016. Ponds on Sable Island in Freedman, B. (Ed.) 2016. Sable Island, the Ecology and Biodiversity of Sable Island. Fitzhenry and Whiteside, Markham ON.

Image gallery

  • Two horses drinking from a pond.
  • Freshwater pond surrounded by dunes covered with vegetation.
  • Aerial view of the ponds and a building near the west tip.
  • A band of black horses take turns drinking from a water hole in the sand.
  • A group of visitors stand on the path at a distance from a horse drinking water from the pond.
  • An aerial view of a fresh water pond on Sable Island.
  • Two ponds surrounded by green vegetation.
  • Horses standing in and drinking from a freshwater pond on Sable Island.
  • A flock of birds fly low over a pond.
  • A flock of birds at the edge of a pond.
  • A large colourful bird standing in the pond.
  • A pond full of pond plants and surrounded by green vegetation.
  • Two researchers standing in the pond surrounded by fog.
  • Cranberry plants stick up out of the water and cranberries float on the top.
  • Large clumps of purple irises next to the pond.
  • Green algae at the edge of the pond.
  • Dried vegetation surrounds a pond.
  • Vegetation covers the site where the pond was.
  • The edge of an icy frozen pond.
  • Two researchers kneel on the sand with a net and some containers.” class=
  • A pond with lots of plants floating on top and sticking out of the water.
  • A researcher stands in the pond to collect samples with a net.
  • A researcher stands in the pond with a hand-held monitoring device.
  • A horse laying down with its feet in the water.

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