It’s more like a slow seepage from below. The lake is being constantly supplied with fresh water from the runoff from the surrounding hills. There are even numerous water falls leading into it.
Not from the salt dome itself, or it would look be like the Lake Peigneur incident.
https://gsa.confex.com/gsa/2007AM/finalprogram/abstract_131360.htm
Seneca Lake is more saline than the other glacially excavated Finger Lakes (e.g., Cl at 140 ppm vs. 40 ppm). Wing et al. (1995) suggested that Seneca, and to a lesser extent Cayuga Lake, has an additional groundwater source of saline water to compliment typical fluvial sources because they are deep enough to intersect the Silurian beds of commercial grade rock salt located ~450-600 m below the surface.
Mass-balance arguments by Halfman et al. (2006) indicated that sodium is stoichiometrically consistent with chloride. Finally, Jolly (2006) showed that the chloride concentration has not been constant over the past century.
Chloride concentrations were ~40 ppm in 1900, rose to ~170 ppm by the 1960’s, and subsequently decreased since 1980 to the present day concentration of ~120 ppm. Here we focus on the decrease in concentration over the past decade.
...A reduction of road salt use, salt mining activities or closure of salt pathways through the sediment column are the probable causes in the annual scale salinity decrease but more work is required to determine the exact cause.