The sur­face area is 104 km². The length of the lake is about 13 km, the width is 11.5 km. The max­i­mum depth, depend­ing on the water lev­el, is 6–10 m. The lake is flow­ing. It is fed by the Tul­dun, Indola, and Zhip­ke­sen rivers. Through the Khor­gin­sky lakes, a small shal­low trib­u­tary of the Kho­la, the Eravnin­sky lakes are con­nect­ed to the Vitim Riv­er. In the south­west­ern part, it is con­nect­ed by a small strait to Sos­novy Lake. The vil­lage of Garam is locat­ed on the shore of the lake. Perch, pike, cru­cian carp, roach, and roach are found here. Peled, bream, and sil­ver bream are also present.

The lake is part of the Eravnin­sky — Khor­gin­sky lake sys­tem, which is locat­ed in the Baikal buffer zone, since these lakes are con­nect­ed not only with each oth­er by chan­nels and ground­wa­ter, but also with the basins of the Uda and Selen­ga rivers, and ulti­mate­ly with Baikal. They are locat­ed on the site of vast ancient lakes of the Meso­zoic era. Three large lakes of the Eravnin­skaya sys­tem: Sos­novoe Island, Bol­shaya and Malaya Erav­na, are close­ly con­nect­ed to each oth­er and are, as it were, one lim­no­log­i­cal whole.
A whole galaxy of small lakes, scat­tered around the main sys­tems of Eravnin­sky lakes, are not con­nect­ed to them and are com­plete­ly iso­lat­ed from any influ­ence of the main mass of large lakes. These include, for exam­ple, lakes: Shchuchye, Gun­da, etc.

The Bol­shoi Eravnin­sky lakes are locat­ed along the cen­tral part of the Eravnin­sky dis­trict. These lakes are of great impor­tance — first­ly, they are a source of drink­ing water for the pop­u­la­tion, sec­ond­ly, a habi­tat for com­mer­cial fish, and third­ly, they serve as a won­der­ful place for recre­ation.