The LKT: Lake Transport Package pane is on the MODFLOW Features tab of the Object Properties dialog box.
It is used for specifying the initial concentration of the lake and either the precipitation concentration, the runnoff concentration, or both.
The pane has three tabs
The Initial concentration tab has a table in which the initial concentration of each chemical species is specified.
The Precipitation concentration tab has a table in which the Starting time, Ending time, and Precipitation concentration.
Starting time and Ending time are explained in the help for the MODFLOW Features tab.
Precipitation concentration is the concentration of solute that enters the lake as precipitation in the MODFLOW Lake package.
The Runoff concentration tab has a table in which the Starting time, Ending time, and Runoff concentration.
Runoff concentration is the concentration of solute that enters the lake as runoff in the MODFLOW Lake package.