Subsurface streams flowing across karst terrain in flat-lying limestones frequently experience subsurface meander neck cut-offs. This paper discusses dye traces that confirmed that the Barren River and Drakes Creek in south-central Kentucky are losing water as part of these streams sink into the limestone and flow across large meanders to resurge at springs downstream. Other examples in west Kentucky and Tennessee will be discussed. Case studies will be presented where a dam was almost constructed at a location on a stream where a subsurface meander neck cut-off would have probably prevented the impoundment of water behind the dam, and at another site where microgravity and dye traces were used to assess the potential for subsurface meander neck cut-offs at a proposed dam site. A third case study will deal with dye traces recently performed to investigate the source of a large boil discharging about 15,000 cfs located about 1800 feet downstream from Jim Woodruff Dam in Florida. Dyes were injected into holes in the bed of Lake Seminole, located by a multi-beam hydrographic survey, about 1500 feet upstream from the dam and traced under a leaky confining layer through the Floridan Aquifer to the boil. Key words: karst, dams, meander, dye trace.