The Fox River Flats IBA comprises a broad expanse of low-lying marshland and intertidal mud flats at the head of Kachemak Bay in lower Cook Inlet. Three major glacial rivers flow into the estuary, depositing layers of silt and clay in a broad fan upon which the Fox River Flats tidal marsh has developed. The Flats are by far the largest marsh in Kachemak Bay, comprising approximately 7,100 acres of coastal marsh and mudflats.
Kachemak Bay is one of the most critical sites for migratory birds in the world; thousands of migrating waterfowl and millions of shorebirds pause along mud flats here each year. The Fox River delta is one of the most significant sites within the bay. On average, over 94,000 individuals of 22 species use this site during spring migration. Fox River Flats is the major spring staging area for geese and ducks in Kechemak Bay . At high tide in both spring and fall, up to several thousand mallards, pintails, scoters and mergansers congregate offshore of Fox River. The upper end of Kachemak Bay, including Fox River Flats, supports 100,000 wintering waterfowl .
Kachemak Bay is recognized as the second most important shorebird staging area in Alaska (following the Copper River Delta). It was designated as an International Shorebird Reserve because it supports greater than 100,000 shorebirds and/or 15 percent of a specie's flyway population on migration. The Kachemak Bay WHSRN site is formed by three main areas: Fox River Flats; Mud Bay and Mariner Park Lagoon; and the Kachemak Critical Zone. ). It has been hypothesized that small shorebirds cannot store enough energy to travel the vast distance from the Copper River Delta to their arctic breeding grounds; therefore, an intermediary stop on the mudflats of Kachemak Bay can be considerably important . Over 600,000 shorebirds have been counted in the Fox River Flats in past years, although numbers have declined somewhat recently [5, 10].
Species of conservation concern that occur but do not meet criteria thresholds include the whimbrel (3- May 1993)and black oystercatcher (4- May 1993)  and trumpeter swans.
Shorebird passage: 1993 = 13,325 to 98,738; 1976 = 1 to 2 million; 1977 = 600,000; 1992 = 7,900 to 35,000.
The flats and lower hillsides between Moose Creek and the mouth of Clearwater Creek are very popular
for hunting and snowmachining. Properties in Fox River Flats, are threatened by residential development and logging pressures.
The Fox River Flats is mostly in state ownership. The flats also have a number of private in holdings that are used by the residents for agriculture and grazing. There is a Russian village and trails that connect the residents to Kachemak Bay on the west side of the Fox River.
Mixed forest; scrub; mudflats/sandflats; standing freshwater; river/stream; blanket bog; water-fringe vegetation.
Notes: patches of salt tolerant plants, such as Lyngby's sedge (Carex lyngbyaei), can be found in poorly drained patches in the upland transition zone. The following sequence characterizes the dominant marsh species (from seaward to upland elevations): 1) Puccinellia grandis (no common name), 2) Ramenski's sedge, 3) Lyngby's sedge, 4) pond aquatic communities 5) inland marsh, and 6) stream banks.
Agriculture-private in-holdings; hunting; nature conservation; tourism/recreation; other-cows and horses are grazed on the flats during the summer.