Linear, one‐dimensional, analytical, and numerical models for seiches (standing waves) existing at the surface and on the internal interface between the upper warm and bottom cold layers for a long, narrow lake are developed. Using the specific bathymetric and thermal structures of a lake, Lake Champlain, these models predict the periods, nodal locations, vertical displacements, and current velocities associated with the fundamental and higher‐order modes. Modeled results are compared with historical limnological data obtained from Lake Champlain. Agreement is good for the periods of the first few modes of the surface and internal seiches; however, predicted current velocities associated with the internal seiche are about half as large as those actually observed.