A
long
time
ago
,
north
America
was
covered
in
____________________
.
As
the
____________________
melted
away
,
they
left
behind
deep
____________________
that
filled
with
water
,
becoming
lakes
.
Because
these
lakes
were
created
together
,
there
are
____________________
that
connect
them
to
each
other
.
Lake
Superior
has
the
greatest
____________________
,
and
because
of
this
there
are
many
____________________
of
fish
that
live
in
the
lake
.
Each
of
the
lakes
has
a
unique
____________________
for
fish
and
other
animals
.
In
recent
years
,
____________________
____________________
have
moved
in
and
hurt
these
unique
____________________
.
Since
we
depend
on
the
____________________
____________________
we
get
from
these
lakes
,
we
must
do
what
we
can
to
protect
them
.
