If you only had 2 small fronds after having had the plant a few years, then it sounds to me as if you may have lost it, sorry I know nothing about aquatic plants, so cannot make any suggestions as regards them, I would suggest that you think about getting a Trachycarpus fortuneii as a replacement for your tree fern, they are quite hardy in all but the coldest areas of the uk, providing you protect them from north and easterly winds, and the older they get, the hardier they get, also after a few years, {depending on what size you buy} you get flowers, which of themselves are nothing to shout about, but the way they are produced is quite dramatic,
look like branches with bunches of tiny flowers. Derek

Hello! The Australian Tree Fern (there are various varieties) generally prefers a moist but warm and sheltered spot, and the recent weather may have affected your plant, including dry weather last two years. A daily mist spray is recommended. I would recommend this as an indoor conservatory plant, out of direct strong light and misted regularly.

those two fronds have since died so I guess I have lost it...