In the third supplemental proceeding, the Ninth Circuit held that Judge Boldt's language, "secondarily in the waters of Puget Sound," meant that the Muckleshoot Tribe's usual and accustomed fishing grounds did not include any areas outside of Elliot Bay.[1] After the decision in United States v. Washington (Washington II),[2] the Muckleshoot Tribe sought to open fisheries in Area 11 of Puget Sound in 1998. Area 11 is a fishing zone that was designated by Washington state regulation after the Boldt Decision. In response to the Muckleshoot's action, the Puyallup Indian Tribe filed a request for determination in district court. The Puyallup Tribe sought a determination that Judge Boldt did not include any areas outside of Elliot Bay (now known as Area 10A) within the Muckleshoot Tribe's usual and accustomed saltwater fishing areas.[3] The district court held that the Muckleshoot Tribe's usual and accustomed saltwater fishing grounds were limited to Elliot Bay. The Muckleshoot appealed and the Ninth Circuit affirmed.

This case required interpretation of the Boldt Decision phrase "secondarily in the waters of Puget Sound."[4] The Ninth Circuit cautioned against applying canons of statutory construction to interpret the Boldt Decision, and affirmed the district court's reliance on the documents actually before Judge Boldt, noting that documents and evidence "play a much larger and definitive role"[5] in interpreting judicial opinions than does legislative history in interpreting statutes. The court concluded that the district court interpreted the Boldt Decision solely on the evidence before Judge Boldt.

The Ninth Circuit agreed with the Muckleshoot's argument that Judge Boldt's use of the broad term "Puget Sound" was "perplexing in light of the geographic precision he generally used in describing [usual and accustomed fishing grounds]."[6] Nonetheless, the Ninth Circuit held that there was no evidence in the record before Judge Boldt to support a saltwater fishery beyond Elliot Bay for the Muckleshoot Tribe. The court analyzed exhibits that were in the record before Judge Boldt, concluding that the exhibits indicated that the Muckleshoot's ancestors were predominantly an upriver people who primarily relied on freshwater fishing. The Muckleshoot Tribe disagreed, citing other exhibits before Judge Boldt, which they argued established Muckleshoot's ancestors had usual and accustomed fishing grounds beyond Elliot Bay. The Ninth Circuit considered this evidence, but came to the opposite conclusion. Most important to the court's consideration of the exhibits was that all references to Muckleshoot saltwater fishing pertained to the Duwamish drainage system, which empties only into Elliot Bay. The facts before Judge Boldt suggested that the Muckleshoot's ancestors only occasionally fished outside of Elliot Bay on their way to collect shellfish and to catch devil fish. The Ninth Circuit held that such incidental trolling could not support a finding of "usual and accustomed fishing grounds."[7]

Finally, the Ninth Circuit rejected the Muckleshoot's argument that findings of fact made by the Indian Claims Commission (ICC) in 1966, involving the Puyallup Tribe, supports a broad reading of the term "Puget Sound" in the Boldt Decision. The ICC had suggested that ancestors of the Muckleshoot used islands in southern Puget Sound. The Ninth Circuit was not persuaded, noting that Judge Boldt previously refused to apply an ICC finding in a case involving the Nooksack Tribe.[8]