The pressure on a swimmer 10 meters below the surface of a lake can be calculated using the formula P = P0 + ρgh, where P0 is the atmospheric pressure, ρ is the density of water, g is the acceleration due to gravity, and h is the depth of the swimmer. From the given atmospheric pressure of 1.01 x 10^5 Pa and the density of water of 1000 kg/m^3, the pressure on the swimmer can be calculated as follows:

P = P0 + ρgh P = 1.01 x 10^5 Pa + 1000 kg/m^3 x 10 m x 9.81 m/s^2 P = 2.01 x 10^5 Pa

Therefore, the pressure on a swimmer 10 meters below the surface of a lake is 2.01 x 10^5 Pa or approximately 2 atm.