There are some industries and products that are very sensitive to sea water or brackish effects, where real data may be needed to protect facilities, etc. I am reminded of the many channel barriers as well as water storage areas on the Francis Marion National Forest which were used to limit salinity reaching rice cultured areas, or release stored freshwater to keep or limit saline or brackish water wedge downstream of critical product areas. The USGS and NOAA uses real time measures of water level reporting in defined locations, and some of these are online. But barring that data being helpful to your circumstance, it is possible to set up monitoring that might be needed to protect your circumstance or need for data to shut down operations to protect equipment or resources. You have probably seen instances where winds from hurricanes adjacent to coastal areas estimate extent of surge or flooding, but the extent of salinity upstream for rivers requires modeling. The best practice for your specific needs would depend on your specific circumstance, the sensitivity of facilities and resources, and availability of nearby data.