Point Source vs. Non-point Source Pollution
Water quality in Lake Granbury is affected by two types of pollution: point source and non-point source. Point source pollution comes directly from a single source such as factory or wastewater plant. This is the type of pollution most people think of when they hear water pollution. This type of pollution, however, has been heavily controlled since the Clean Water Act was passed in 1972. Regulations regarding point source pollution place limits on how much and what kind of pollutants can be discharged. While this has not eliminated industrial or domestic waste pollution from entering our waters completely, it has reduced what once was our biggest source of water pollution.
Non-point source (NPS) pollution is more difficult to isolate and control. The sources are often hard to identify. This type of pollution comes from the cumulative effect of a region's residents going about their everyday activities, such as driving a car, fertilizing their lawn, or spraying pesticides. NPS pollution is caused by rain moving over the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into rivers and lakes. Much of the water quality concerns with Lake Granbury are associated with non-point source pollution.
A considerable portion of the development around the lake is located on man-made canals and coves. These coves are shallow, dead-end bodies of water with little mixing or interaction with the main body of the reservoir. Many of these developments rely on on-site sewage facilities (OSSF). There are approximately 9,000 of these systems around Lake Granbury many with absorption fields installed on small lots in close proximity to the lake. When the systems fail due to age or lack of maintenance, bacteria contamination can occur in surrounding waterbodies.
Periodic elevated concentrations ofE. coliand fecal coliform bacteria have been found in many of the coves and canals of Lake Granbury. A multi-pronged study was conducted conducted during the development of the Watershed Protection Plan to evaluate the potential sources of the bacterial contamination. The study indicated that in many areas much of the bacteria levels can be attributed to near-canal sources such as OSSFs and pet waste. A few other areas indicate livestock and wildlife as the primary contributing factors to high bacterial levels. While the highE. colilevels in and around these developments have yet to affect the main body of the lake, they are still of concern due to the recreational activities that occur in the canals. The Watershed Protection Plan was developed to address these causes pollution.
Much of the nutrients that enter our waterways come from non-point sources. Fertilizers supply nutrients to lawns and crops. When fertilizer is applied excessively or just prior to a rainstorm, it washes off the lawn or field and into the gutter, where it makes its way through the storm sewer system and creeks and into the lake. Once in the water, these nutrients have the same effect on algae as they do on lawns - they make it grow! Excessive algae can have devastating effects on lake or stream, consuming all the oxygen and suffocating fish and other aquatic wildlife. Increased awareness of alternative practices such as xeriscaping and using native grasses can help cut down on fertilizer use. Chlorophyll-ais the pigment found in algae. When concentrations of chlorophyll-aincrease so does the concentration of algae found in the lake. Increased algae in the lake can result in low dissolved oxygen concentrations, fish kills, and increased treatment cost. Lake Granbury has been listed in the 2010 Texas Integrated Report as alake with a "concern for water quality" based on a chlorophyll-ascreening level.