Magistrates heard how in October 2003 Environment Agency officers had made the developers aware of potential drainage problems on their housing site off the A58 in Ripponden.
Officers were concerned that silt from the site could end up draining into the nearby River Ryburn and asked Persimmon Homes to take action to prevent this.
The company applied for a Consent to Discharge permit which regulated the amount of effluent from the site that could go into the watercourse.
However, in July 2005 the Environment Agency received a report of silt in the River Ryburn, and a sample showed that there was 48 times more suspended solids, such as silt particles, in the water than the amount allowed under Persimmon Homes permit.
Ms Fogg said the sample revealed 2,420 milligrammes of suspended particles per litre rather than the consented level which was 50 milligrammes per litre.
In interview, the company explained that it had a number of holding tanks to prevent run-off from the site going directly into the river. But run-off had escaped when a stopper came loose during bad weather.
In the second incident in May 2006 an officer inspected the site and found more pollution had discharged into the river. A sample showed the amount of suspended solids was again more than the permitted amount at 664 milligrammes per litre.
The court heard that although Persimmon Homes had the equipment to contain the discharge, there was only limited checks to see if it was working properly.
In both incidents, the river’s wildlife was not visibly affected, but the pollution could have had a damaging impact.
After the court case an Environment Agency officer Dave Tempest said: Persimmon Homes was warned of the risk of pollution to the river yet failed to take all the necessary precautions.
Rivers in West Yorkshire are recovering from their industrial legacy and it is vital that businesses take responsibility for their actions and ensure that the environment is protected.