Was it the worst episode in Star Trek history?
I think it's probably the most silly and idiotic episode in Star Trek history but it is way too entertaining to be the all time worst episode.
I think out of the numerous plot holes in that episode the most amusing one was that Tom Paris successfully created the warp 10 device that can travel everywhere and worked perfectly and the only side effects is something that can be cured easily by The Doctor (that the medical treatment was so inconsequentially easy that it was done Off Screen in a log report which kinda undermines every medical drama in Star Trek history if the doctor is able to cure someone changing species so easily). Voyager for some reason to abandon the device even though it's can bring them home with no problems at all.
Regarding the salamanders yes I find it funny they just abandoned it even though they are human and especially considering that in the long trip home, the idea of procreation is actually important.