<p>Rapid environmental changes can lead to the degradation or loss of the breeding habitats of birds. This study investigated the effects of environmental changes in rivers on the breeding sites of the Long-billed Plover (<i>Thinornis placidus</i>), a ground-nesting shorebird that breeds on open, sparsely vegetated sand and gravel bars along rivers. From April to July 2020 and in June 2021, we surveyed 42 historical breeding sites (sand/gravel bars) where Long-billed Plovers were reported to have bred between 2012 and 2015. At each historical breeding site, we recorded plover presence/absence, the current habitat status, and the causes of any habitat loss. We also examined 21 historical breeding sites to analyze changes in substrate composition, area, width, length of the sand/gravel bar, and stream width. Of the 42 sites, 69% were lost primarily due to vegetation encroachment. The remaining 31% retained suitable habitat conditions, of which 62% were occupied by plovers. Environmental assessments of 21 breeding sites revealed a decline in sand proportion, an increase in rock and other substrates (e.g., litter and twigs), and a reduction in sand/gravel bar areas. The rate of breeding habitat loss due to vegetation encroachment varied between river systems, which was ascribed to the influence of stream width and flow and dams. The decrease in suitable substrate and shrinking sand/gravel bars suggest declining habitat quality for breeding. Our findings provide information for the selection and management of breeding habitat reserves for the Long-billed Plovers.</p>