There
are two main types of lakes in the Hamilton area, Lake Ontario, a
large deep lake, and smaller inland lakes, many of which are reservoirs
created artificially through the damming of rivers and streams.
Lake Ontario
Lake
Ontario is a large, freshwater lake. It is very deep, 86 metres
on average and 245 m at its deepest, but it has the smallest surface
area of the Great Lakes (18 960 km2). Nonetheless, it has the largest
watershed area relative to its surface area of all the Great Lakes.
| A
watershed is an area of water drainage bounded by a
relatively high topographic margin known as the drainage "divide".
Water falling anywhere within the boundary of a watershed
is ultimately directed to one outlet. The terms 'catchment'
and 'drainage basin' mean the same thing as watershed. |
Eighty
percent of Lake Ontario's water originates in Lake Erie to which
it is naturally connected by the Niagara River, made famous by Niagara
Falls (a drop of almost 100 metres). The Welland Canal was built
to allow ships to go between the two lakes and bypass the falls.
The remaining water in Lake Ontario comes from tributaries in its
watershed (rivers and streams, 14%) and from precipitation directly
on its surface (7%). Lake Ontario's outlet is the St. Lawrence River,
to which it loses 93% of its outflowing water. The remaining 7%
is lost through evaporation.
Lake
Ontario at Confederation Park. Photo by Betty Blashill.
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Lake
Ontario is also the recipient of materials flowing through the entire
Great Lakes chain because of its position at the end of that chain.
This means that it is impacted by human activities throughout the
entire Great Lakes watershed. Several organisations are now engaged
in serious efforts to restore and monitor the Great Lakes ecosystems,
including Lake Ontario.
Small Inland Lakes
There
are other smaller lakes in the Hamilton area that are mainly the
result of river damming, either to control flooding or to regulate
stream flow. When a lake is formed in this way it is called a reservoir.
Examples of reservoirs in the Hamilton area include the Binbrook
Reservoir, Christie Lake, and the reservoir at the Valens Conservation
Area. These lakes are managed by the Hamilton Conservation Authority.
They are stocked with fish and have chlorinated swimming areas separated
from the main water area. Some of them have wetland areas on their
margins.
In Halton region, most lakes are also reservoirs, like the Mountsberg
Reservoir, but there is one rare, natural lake, , located on top
of the Niagara Escarpment called Crawford Lake.
Crawford
Lake. Photo courtesy of Conservation Halton.
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This
lake formed in a deep fissure in the escarpment rock. This fissure
is deep enough that the water near the bottom does not get any sunlight
and is very cold. This cold bottom layer does not mix with the warmer
upper water layer, making this lake 'Meromictic'.
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Most
lakes have a warmer, upper layer, the epilimnion, and a
colder, lower layer, the hypolimnion. Lakes are stratified
into these layers because warm water is less dense and heavy
than cold water. As the surface water warms over the summer
this warmer water stays near the surface and the cooler
water stays near the bottom. This is called 'thermal
stratification'.
These
layers mix with each other when the upper water layer cools
in the fall and sinks, forcing the water near the bottom
towards the surface. Lakes that freeze over in the winter
mix again in the spring as the upper ice layer melts and
this very cold water sinks to the bottom. This
mixing of the layers is called 'turnover'.
Lakes
that have extremely cold lower layers, as happens in very
deep lakes, do not mix completely are called 'meromictic'.
They usually have such low oxygen levels in the cold, lower
hypolimnion layer that decomposition is greatly limited.
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