A pump monitoring system, comprising a controller configured to: determine a value for motor power indicative of pump performance; determine a value indicative of at least one of water velocity through the pump and motor speed; calculate a pump load coefficient using the value indicative of pump performance and the value indicative of at least one of water velocity through the pump and motor speed to produce a calculated pump load coefficient, wherein the calculated pump load coefficient is indicative of a blockage of a drain in a liquid holding tank, the drain being coupled to an input of the pump wherein the pump load coefficient is calculated based on the equation: K lc = P / V 3 where K lc is the pump load coefficient, P is the value indicative of the motor power of the pump, and V is the value indicative of at least one of water velocity through the pump and motor speed; the controller being further configured to: filter the calculated pump load coefficient using a first time constant to produce a filtered pump load coefficient; filter the calculated pump load coefficient using a second time constant to produce a filtered floating threshold value, the second time constant being greater than the first time constant; detect a blockage of the drain when the filtered pump load coefficient is less than the filtered floating threshold value for a first defined period of time and at the same time or subsequently: calculate a difference between the calculated pump load coefficient and a previously calculated pump load coefficient; detect a blockage of the drain when the difference is less than a threshold for a second defined period of time; and adjust an operation of the pump based on the detected blockage. determine a value for motor power indicative of pump performance; determine a value indicative of at least one of water velocity through the pump and motor speed; calculate a pump load coefficient using the value indicative of pump performance and the value indicative of at least one of water velocity through the pump and motor speed to produce a calculated pump load coefficient, wherein the calculated pump load coefficient is indicative of a blockage of a drain in a liquid holding tank, the drain being coupled to an input of the pump wherein the pump load coefficient is calculated based on the equation: K lc = P / V 3 where K lc is the pump load coefficient, P is the value indicative of the motor power of the pump, and V is the value indicative of at least one of water velocity through the pump and motor speed; the controller being further configured to: filter the calculated pump load coefficient using a first time constant to produce a filtered pump load coefficient; filter the calculated pump load coefficient using a second time constant to produce a filtered floating threshold value, the second time constant being greater than the first time constant; detect a blockage of the drain when the filtered pump load coefficient is less than the filtered floating threshold value for a first defined period of time and at the same time or subsequently: calculate a difference between the calculated pump load coefficient and a previously calculated pump load coefficient; detect a blockage of the drain when the difference is less than a threshold for a second defined period of time; and adjust an operation of the pump based on the detected blockage. filter the calculated pump load coefficient using a first time constant to produce a filtered pump load coefficient; filter the calculated pump load coefficient using a second time constant to produce a filtered floating threshold value, the second time constant being greater than the first time constant; detect a blockage of the drain when the filtered pump load coefficient is less than the filtered floating threshold value for a first defined period of time and at the same time or subsequently: calculate a difference between the calculated pump load coefficient and a previously calculated pump load coefficient; detect a blockage of the drain when the difference is less than a threshold for a second defined period of time; and adjust an operation of the pump based on the detected blockage. calculate a difference between the calculated pump load coefficient and a previously calculated pump load coefficient; detect a blockage of the drain when the difference is less than a threshold for a second defined period of time; and adjust an operation of the pump based on the detected blockage.