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The rise to prominence of total maximum daily loads in the 1990s has led to the identification of numerous water bodies where phosphorus (P) has been identified as the leading cause of impairment, thereby giving new impetus to P control at WWTPs. One control action considered for 2 TMDLs for segments of the N. Bosque River in 2001 was implementation of P controls at 6 wastewater treatment plants (WWTPs) designed to meet ending effluent standards of 1 mg/L total P. P controls are a particular concern for small communities, where unit removal costs are typically much higher than for larger WWTPs. P removal was estimated to cost $5.19/person/yr for the largest community (population 15,000), while it ranged from $16/person/yr to $152/person/yr for the smaller communities (populations ranging from 360 to 3,500). Cost per unit P removal is also considerably lower at the Stephenville WWTP ($31/kg) versus the smaller plants, whose costs ranged from $101/kg to $729/kg P removed. High unit costs for the small WWTPs is due mainly to high capital costs in relation to their small size. The great disparity in unit costs suggests that P control obligations (or credits) could be traded among the six N. Bosque WWTPs to mutual advantage. The most optimal trading scenario would have the control obligations of the three smallest WWTPs transferred to the Stephenville plant thereby allowing the small WWTPs to operate without P control. This trading scenario results in estimated savings of $188,000 annually for the four trading WWTPs.