Updated. No one expected this so soon after Montana approved the CSKT Water Compact. Beginning 28 May, the Swan River’s streamflow (discharge) dropped below the Minimum Enforceable Flow set by the compact (Appendix 26 PDF). In theory, once the compact is in force, the CSKT could issue a call on irrigators in the Swan Valley to protect instream flows, but in these circumstances I think it unlikely that a call would be made.
Here’s the hydrograph: