Fungi can categorized as both,  aquatic and terrestrial.
It has been hypothesized that most aquatic fungi evolved from terrestrial fungi whose spores frequently landed in streams. As a result of this evolutionary history, several genera of fungi, such as Ascotaiwania and Annulatascus, include both terrestrial and aquatic species (Wong et al., 1998). Although they may be scary for leaves, aquatic fungi are looked upon pretty favorably by the other stream dwellers. And this, for a leaf, must be a very frightening prospect. A daunting collection of leaf-eating fungi lurks in the waters of freshwater streams. A few are basidiomycetes or oomycetes, but most are ascomycetes and their asexual stages. These fungi are aquatic ascomycetes. Penetrating their substrates, aquatic ascomycetes release enzymes that break down the ligno-cellulose of plant cell walls, the pectins that hold cells together, and starch stored in plant tissues. The fungi then use the resulting simple sugars and amino acids to grow.  The fungi are readily trapped from bodies of water, soil, or from surfaces where a water film forms transiently. The importance of chytrids in aquatic habitats is only now becoming clear. Chytrid DNA is closely associated with processes of removal of picoplankton in lakes and large water bodies. Conditions in fresh water are markedly different to those in the ocean. The open sea has quite different salinity to salterns where the water is slowly evaporating. Sometimes the water is extremely acidic or toxic. Fungi are found in all these environments. Mycomycota is the name for the fungi in lichens. Lichens are composed of fungus and algae in a symbiotic relationship, as the algae provides nutrients, while the fungus protects it from the elements. Lichens photosynthesize light, with photoautotrauphs located near the surface of the fungi. They are crucial decomposers, feeding on living and decaying organisms. They live in aquatic and semi-aquatic environments (even damp soil), in both salt and freshwater bodies of water. They are distinguished by their flagellated spores or gametes, which help the reproductive units repel through water. Aero-Aquatic Hyphomycetes: Ingoldian fungi are not the only fungal inhabitants of litter. Another group form large coiled or rounded conidia which trap air, and these are known as aero-aquatic hyphomycetes. The advantage of their spores is that when the water dries, spores can lodge in the mud. Conditions in fresh water are markedly different to those in the ocean. The open sea has quite different salinity to salterns where the water is slowly evaporating. Sometimes the water is extremely acidic or toxic. Fungi are found in all these environments. Other fungi grow with algae and cyanobacteria forming lichens. Fungi can be detrimental in that some fungi cause plant diseases that cause the loss of economically important crops. (For more on plant fungal diseases, click here.) Fungi can also cause animal (humans included) diseases. Classically, the following groups have been considered fungi: 1) slime molds have a feeding phase of the life cycle (the trophic phase) that are motile and lack cell walls. Food particles are ingested. 2) aquatic fungi have cell walls and absorb nutrients rather than ingest them. The sex cells and spores of aquatic fungi are motile (zoospores). Oomycetes (water molds) Chytridiomycetes (unicellular chytrids). 3) terrestrial fungi have cell walls and absorb nutrients rather than ingest them. The sex cells and spores are not motile (zoospores). Zygomycetes (e.g. black bread mold, animal dung fungi) Ascomycetes (e.g. cup fungi, truffles) Basidiomycetes (e.g. mushrooms or toadstools, puff balls, rusts, smuts) Baker's yeast or Saccharomyces cerevisiae, a unicellular fungus, is used to make bread and other wheat-based products, such as pizza dough and dumplings. Yeast species of the genus Saccharomyces are also used to produce alcoholic beverages through fermentation. 1 With plants: Fungi have a cell wall and vacuoles. 2  They reproduce by both sexual and asexual means, and like basal plant groups (such as ferns and mosses) produce spores. 3  Similar to mosses and algae, fungi typically have haploid nuclei. However, it is often unclear whether such fungi,lacking typical morphological adaptations, are terres-trial or truly aquatic. For example, species of Asper-gillus and Penicillium are among the most commonfungal isolates from terrestrial, freshwater, and marineenvironments, even from deep-sea sediments. Inaddition to lichens, zoosporic fungi and fungal-likeorganisms are found in supralittoral soils (Sparrow1968 and references therein, Ali & Abdel-Raheem2003). ‘Aero-aquatic’ fungi form another group ofmitosporic fungi adapted to frequent drying and wet-ting cycles (Webster & Descals 1981). Aquatic fungi, in the broadest sense, include fungi present transiently in water, terrestrial fungi that release spores which are dispersed in water, and species that function entirely within water. Water is found in transient pools after rain, swamps, estuaries, permanent rivers and oceans. Conditions in fresh water are markedly different to those in the ocean. The open sea has quite different salinity to salterns where the water is slowly evaporating. Sometimes the water is extremely acidic or toxic. Fungi are found in all these environments.
http://blog.mycology.cornell.edu/2008/08/24/fungi-in-streams-a-leaf-nightmare/ http://fungi.life.illinois.edu/about/intro http://bugs.bio.usyd.edu.au/learning/resources/Mycology/Habitats/aquaticFungi.shtml http://faculty.college-prep.org/%7Ebernie/sciproject/project/Kingdoms/Fungi%207/fungi%20website/evoltuion.html http://bugs.bio.usyd.edu.au/learning/resources/Mycology/Habitats/aquaticFungi.shtml http://education.stonehill.edu/fieldguide/Field_Guide/Main/fungus.htm https://en.wikipedia.org/wiki/Fungus http://www.int-res.com/articles/ame_oa/a059p125.pdf http://bugs.bio.usyd.edu.au/learning/resources/Mycology/Habitats/aquaticFungi.shtml
are fungi aquatic or terrestrial