228 
There is evidence that in 1942 the 
growing season at Ridge Lake began un- 
usually early. The average weekly water 
temperatures (at + feet) of 62.6 degrees 
F. recorded for the week of April 20-26, 
70.2 degrees F. for April 27—May 3, 
and 82.5 degrees F. for June 1-7 are un- 
usually high for these times of year, fig. 5. 
Further, the first schools of bass fry in 
1942 were seen on May 14 and the maxi- 
mum number of schools was counted on 
May 19. In all other years except 1941 
and 1951, schools of bass fry were not in 
evidence until after June 1. For these 
reasons, we considered that the 1942 sea- 
son was abnormally long. In most years 
of this study, the growing season at Ridge 
Lake did not exceed 6 months. 
Aquatic Plants.—A large number of 
marsh and moist-soil plants were to be 
found growing along Dry Run Creek 
before Ridge Lake was built. In March, 
1941, prior to the closure of the gate 
valve in the dam, G. H. Boewe and 
Frank C. Bellrose of the Illinois Natural 
History Survey staff collected plants in 
the lake basin and reported on the species 
to be found there. Among the marsh 
plants were the following: 
Bulrush, Scirpus atrovirens Willdenow 
and Scirpus, probably polyphyllus 
Vahl 
Common cattail, Typha latifolia Lin- 
naeus 
Horsetail, Equisetum sp. 
Sandbar willow, Salix interior Rowlee 
Sedges, Carex spp. 
Virginia wildrye, 
Linnaeus 
Early in the period of impoundment, 
from April, 1941, until midsummer, 1942, 
little aquatic vegetation was in evidence, 
although cattail, American waterplantain, 
Alisma subcordatum Rafinesque, horsetail, 
and some sedges had appeared at the up- 
per end of the lake. Leafy pondweed, 
Potamogeton foliosus Rafinesque, was col- 
lected in several places in the upper end 
of the lake on September 5, 1942, and by 
September 15 it was becoming abundant. 
In 1941 and subsequent years, any cat- 
tails that appeared were cut off at the 
roots. Consequently, in the years that 
the lake has existed, these plants have 
never increased in abundance beyond a few 
scattered individuals. 
Elymus virginicus 
Ittinois NaturAL History Survey BULLETIN 
Vol. 26, Art. 2 
Scattered bunches of Potamogeton foli- 
osus were growing in the shallows in front 
of the surtace spillway and in the upper 
end of the lake in early June, 1943. By 
August, dense mats of fine-leaved pota- 
mogeton were abundant in water up to 6 
feet in depth, and scattered bunches of 
P. nodosus Poiret, sago or fennelleaf pond- 
weed, P. pectinatus Linnaeus, cattail, 
waterplantain, and several species of ar- 
rowheads, Sagittaria spp., including com- 
mon arrowhead or duck potato, 8. lati- 
folia Willdenow, were growing in shallow 
water. 
In 1944 and 1945, the vegetation was 
essentially of the same species as those 
found in 1943; in addition, the naiad, 
Najas flexilis (Willdenow) Roskovius & 
Schmidt, and Canada waterweed or elodea, 
Anacharis canadensis (Michaux) Plan- 
chon, were first collected in 1945. 
In 1946, a vegetation die-off occurred 
for the first time in Ridge Lake. A simi- 
lar die-off, which occurred each year from 
1946 on, usually had begun by the tenth 
of July. A coating of blue-green algae 
seemed to envelop the plant mats, which 
began to sink in some places, forming deep 
ravines of open water between ridges of 
dying plants. “These open-water areas 
gradually increased in extent until much 
of the lake that had been choked with 
vegetation in June was open water by 
the end of July. 
In 1948, when among the most a- 
bundant plants were sago pondweed and 
elodea, these plants completely disinte- 
grated within 2 weeks of the time they 
were first observed to be affected (July 
8). Dragging a garden rake on parts of 
the lake bottom, where the thickest mats 
had been, produced only wisps of decaying 
plant stems. By July 23, the entire lake 
was open water except for small beds of 
elodea in shallow water at the upper end 
of the lake and at the surface spillway. 
These were second-growth plants, as the 
original plants had died there also. Both 
sago pondweed and elodea gradually came 
back, until by August 25 the plants had 
grown to the surface again in much of the 
area formerly filled with them. However, — 
the growth was not so thick as the first 
growth had been. 
In 1949, when the lake refilled only to 
about the 11-acre contour after the March ~ 
