142 BULLETIN UNIVERSITY OF MONTANA 
springs up from the south, increasing until early in the afternoon. To- 
ward evening the lake becomes quiet. About dusk a light breeze blows 
out on the lake from the mountains. At the laboratory the evening 
lake breeze is from the east. We have often watched the ripples mov- 
ing across the water toward our boat, coming from the land, as we were 
at work with the pump. The mountains cool quickly, the cool air flow- 
ing down the sides and across both the valley and lake. Similar pheno- 
mena have been noticed on all the lakes of the region. 
Opposite Wild Horse Island the lake is widest, here having a total 
extent across of 18 or 19 miles. This island rises several hundred feet 
out of the lake, and is almost entirely in the western arm, projecting out 
from the main body of the lake. From the contour of the mainland it 
is possible for winds to blow up the lake from the lower end, and across 
the lake from the western arm. ‘These air curents often meet in the 
open lake east of Wild Horse. Here the wind is most uncertain and the 
lake roughest. Winds blowing either up or down the lake may meet 
other winds from the bay.. South of the islands the lake is rarely rough. 
But when the lake gets real bad it seems as though Neptune was in a 
rage and had stirred up the waters to the bottom. In ten minutes the 
lake may change from a perfect calm to a sea on which small boats will 
hesitate to go, and which may even keep the larger boats in harbor. The 
surf beats as in larger lakes. One morning we started home in a 32- 
foot steamer. A mile out large waves were met coming up the lake which 
caused us to turn back to keep from getting our valuable material and 
specimens wet. Three days after a second start was made. We hugged 
shore for six miles, when the strong wind piled the waters so high we 
sought the shelter of Wood’s Bay. Before we could get to shelter the wind 
died down so the journey could be resumed. When half way down and 
we were congratulating ourselves on crossing the widest part without 
trouble, a wind sprang up which increased in a few minutes to such pro- 
portions that the pilot was wet from head to foot, and we were obliged 
to seek shelter behind the nearest land, an island. In about three hours 
the journey was resumed. In the evening the lake was quiet. 
During the summer, June, July and August, the lake is comparatively 
quiet, and the winds as given above generally prevail. In spring and 
fall they are uncertain, and may come up strongly from any quarter in 
a short time. On the occasion mentioned when waves turned us back 
after starting homeward the waters were driven by a strong south wind. 
On entering the harbor, the mouth of Swan river, a little over a mile of 
travel, a light breeze blew from the north east, apparently from the 
mountains. All day the waves rolled, but subsided toward evening. 
As a result of these conditions small boats work close in shore. Row 
boats seldom go far out in the lake. To attempt to cross the lake in one 
would be very unwise. Fatalities do not occur because people are care- 
ful. As most of the residents are unfamiliar with boats in rough water 
and necessity does not drive them on the lake there are not likely to be 
reckless or foolish trips in rough water. 
In the summer of 1902 a dam was constructed across the river at the 
outlet of the lake. This dam was made ag follows. Piles were driven 
