GPX would be as close to a "standard" format as you will find. There are programs that will do the conversion if required.
Garmin WPs can be saved to SD card as either GPX or ADM files. Can I simply stick SD card into Lowrance and export WPs over? Haven't bought Lowrance yet so can't try it out.
It has always been my private conviction that any man who pits his intelligence against a fish and loses has it coming. ~John Steinbeck
GPX would be as close to a "standard" format as you will find. There are programs that will do the conversion if required.
Download GPSBABEL and you'll be able to convert your files easily. Lowrance uses GPX but the header information might throw it, I've done the reverse, Lowrance to Garmin.
Depending on how many marks you have the freeware version of GPS Utility will do it. No need to "convert"--you simply import the original marks in, then click Save As> .usr. job done, Lowrance uses .usr file format.