Large lakes like Lake Ontario seem mysterious because they are so deep that it seems impossible to imagine what is happening below the surface. More easily seen is the shoreline that is important habitat for many plant and animal species. It is largely because people have come to realise the value of shoreline habitats for wildlife that the restoration of much of the Great Lakes has occurred.

In some areas the shore is rocky and there is little sediment to support plant roots, but in many areas there is a gradually sloping shoreline. In these shallow areas plants are able to grow roots down into the lake sediment, stabilising the shoreline and forming coastal marshes. Plants that do this effectively are cattails (Typha spp.) and bulrushes (Scirpus spp.). This is the most productive zone of the lake, where fish spawn and birds nest.

Red-necked Grebes feeding young. Photo by Barry Cherriere.

Shorebirds, ducks and geese in particular take advantage of shoreline habitat, foraging at the lake edge. Some even nest nearby. In the restored areas of Hamilton Harbour you can find terns (e.g. Sterna caspia, the Caspian Tern), gulls (e.g. Larus marinus, the Great Black-Backed Gull), Double-Crested Cormorants (Phalacrocorax auritus), ducks (e.g. Anas rubripes, the American Black Duck), and Osprey (Pandion halietus).

Red Head Ducks flying over Lake Ontario. Photo by Barry Cherriere.

You can also find fish and their eggs here. Native fish species such as Northern Pike (Esox lucius), Bowfin (Amia calva), Freshwater Drum (Aplodinotus grunniens), Pumpkinseed (Lepomis gibbosus), and Yellow Perch (Perca flavescens) can all be found here at some time in their life cycle.

Northern Pike. Photo by Mike Giovanetti.

Invasive fish species are also abundant, including the Carp (Cyprinus carpio) and Alewife (Alosa pseudoharengus).

In the deeper, cooler waters offshore, other species of fish are more common. These include the non-native Rainbow Smelt (Osmerus mordax) and the native Burbot (Lota lota), Lake Trout (Salvelinus namaycush) and Lake Whitefish (Coregonus clupeaformis).

Offshore waters are not the home for many birds, but many hunt for food farther out than you might expect, including gulls, terns and cormorants.

Plants are also of interest in lake habitats. Because Lake Ontario is so deep, not enough light reaches the bottom to allow plants to grow there. Instead, small plants called algae are present, floating freely with the currents. Algae are often referred to as phytoplankton.

Daphnia ambigua, a zooplankton, is one of the smallest species of Daphnia in North America. It is common in lakes and permanent ponds in southern Canada. Photo by Chad Rowe and Paul Hebert, Cladoceran Web Site, University of Guelph. www.cladocera.uoguelph.ca.

They share the water with free-floating animals called zooplankton, 'zoo' meaning animal. Together they form the basis of the aquatic food chain. Both insects and fish eat plankton, and in turn they are eaten by other fish, birds and mammals — including us!

All lakes, including reservoir lakes, have plankton. In fact an overabundance of phytoplankton is one sign that there is too much organic pollution, such as sewage and domestic water, going into the lake. Lakes like this appear green because they have so much algae and are called 'eutrophic'.

Lakes that are clear, without too much algae, are called 'oligotrophic'.

While there are some naturally eutrophic lakes and rivers, most are oligotrophic by nature.