e- . lakes at elevations above 2,000 feet. 
Fifty-one percent of these lakes were 
:h i' found to be acidified to a pH of 5 
ay or less, and 90 percent of those found 
« acidified had no fish. Some of those 
ed I lakes supported fish forty years ago. 
jh ' Studies made in the 1970s in Canada 
ed - also show that lakes in certain areas, 
of ranging from southwest Ontario east- 
ta- I ward to Nova Scotia, are losing all 
their species of fish. 
Levels of pH and alkalinity taken 
m I from the 1930s through the 1950s are 
er- I now considered unreliable because the 
ole I methods then used for analysis put 
re- I chemicals into the water to produce 
ion I a color indicator of acidity and alka- 
pH I linity, and that process altered the 
ide. I variables being measured. Electronic 
the I methods of measurement have re- 
dai I placed the old techniques, but the un- 
nge I reliability of the old data has caused 
jut I some people to question whether or 
the I not acidification has occurred at all. 
v jv( I They suggest that perhaps the lakes 
1 0 « were always acidified. The biological 
5 in I data, however, are an independent and 
;aC fc reliable indicator of acidification. Fish 
I have disappeared from numerous 
;nE , I lakes and streams that are reported, 
. I on the basis of measured chemical 
i change, to have become acidified. Fish 
have also disappeared from hundreds 
of bodies of waters for which no chemi- 
cal data from an earlier period are 
available. These waters are now too 
acidic and their aluminum concentra- 
tions too high for fish to survive. When 
fish are stocked in such lakes, they die. 
It’s hard to argue with a dead fish. 
The futility of stocking such waters 
is illustrated by the history of Lake 
Colden, a small lake at an elevation 
of almost 3,000 feet in the heart of 
the Adirondack Mountains. Described 
as a fisherman’s paradise, Colden was 
one of the best trout-fishing lakes in 
the area but the annual catch declined 
from the 1950s through the 1960s. 
Efforts to stock the lake in the 1960s 
met with failure; the new fish died 
quickly. The last fish disappeared in 
1970. 
The food supply available to fish 
in lakes is greatly altered as acidi- 
fication proceeds. In those lakes hav- 
ing a pH from 5 to 6 — a range in 
which the ionized hydrogen level has 
a marginally negative effect on 
trout — there are significant changes 
in the availability of different species 
of zooplankton (microscopic organ- 
isms suspended in the water), insects, 
other aquatic invertebrates, and 
Lake Colden in the Adirondacks, 
once highly prized by trout 
fisherman, is now so acidic that 
fish cannot survive in its waters. 
plants, all of which serve as food for 
some fish. The number of zooplankton 
species declines with decreasing pH 
levels as was demonstrated in my work 
involving large-scale surveys of Nor- 
wegian lakes. Scientists at the Uni- 
versity of Bergen, in Norway, eval- 
uated the biomass, or weight, of 
bottom-dwelling invertebrates in three 
lakes with a pH range of 4.3 to 4.7 
and five lakes with a range of 5.8 
to 6.2 and found less food available 
to fish in the more acidic lakes. Al- 
though the availability of fish food 
organisms has been found to decrease 
in some acidified lakes, the effects 
of these changes on fish life have not 
been investigated. 
Some of the invertebrates that are 
the normal elements of a fish diet 
have a low tolerance for acid and can- 
not be found below a pH level of 6. 
Such is the case with the tadpole 
63 
