The waterfall is named on Googel maps as Skaftárhreppur waterfall but I can’t find an official name. I also found a picture with the name Selárfoss, but I also can’t find the name of the river. Because it is an Icelandic waterfall I named it Skaftárhreppur foss.
In 2011 (the last time I was in Iceland) I was nearby but I didn’t knew that there was a waterfall. Skaftárhreppur foss is located along road F206, not far from the crossing road 1>F206 at Kirkjubæjarklaustur. From road 1 it is a 7 kilometer drive over road F206. I think it is no problem tot take the road (in summertime) until Skaftárhreppur foss. If you want to go further to Fagrifoss, you need a 4WD.
I like the pictures of Skaftárhreppur foss very much. It had an unusual shape and the viewpoint you have are amazing. This is definitely a waterfall you should visit!