According to history, Bear Lake and Bear River received their names from a trapper by the name of Donald MacKenzie who headed a group of 55 men and 195 horses from the Canadian Northwest Fur Company.
They arrived in Bear Lake Valley during the year of 1818. MacKenzie and his men found so many black bears around the lake and along the river that it was named Black Bear River.
Bear Lake is an old lake. The lake basin was formed during the growth of the surrounding mountains.
Since that time, a lake has been present whenever the climate has been wet enough, but it was probably completely dried up during a very dry period.
About 5,000 years ago, the Bear Lake filled the entire valley, which is about 50 miles long by 8 to 12 miles wide. The present lake occupies only the southern end of the valley.
It is just less than 20 miles long and 4 to 8 miles wide. As the lake became smaller, a large marsh formed at its northern end. This is known as Mud Lake today.
Bear Lake is deepest along the east side. The greatest depth found during this study is 208 feet below the present shore, but more than half the lake is deeper than 100 feet.
The north, northwest, and south shores are sandy beaches. Much of the rest of the shoreline is rocky.
Beyond the rocks, the bottom is sand to a depth of about 25 feet. From 25 to 75 feet, the sand is gradually replaced by silt and marl, and below 75 feet the bottom is a fine, gray silt marl.
Usually, the lake is quite clear, except when muddy water from Bear River is entering at the north end. Its characteristic blue green color is caused by large amounts of carbonates in the water.
By late summer, the surface water usually warms up to about 70 degrees. This warm water extends down about 30 to 50 feet. Below that, the water cools rapidly and the water below 150 is usually never warmer than 42 degrees. The lake usually freezes over about four years out of five, according to Utah Power and Light Company records. A complete ice cover usually comes in late January or early February, and breaks up in April.