Shipwrecks and potentially live ammunition dumps could litter the intended route for the proposed new energy interconnector across Bass Strait.
They will potentially lead to tweaks of the 250 kilometre undersea cable route for the $3.5 billion Marinus Link between Heybridge in North-West Tasmania and Waratah Bay in Victoria.
"All ammunition dumps should be considered live and appropriate safety measures taken," Cosmos Archaeology said in desktop analysis for Marinus Link lodged with the federal Environment Department as part of the assessment process.
"There are two ammunition dumps and one boat dump located in the study area and surrounds.
"The ammunition dumps include projectiles, depth charges and three 'various' dumps, including generators, fuses, igniters, shells, flares and cartridges.
"Due to the relatively recent timing of these dumping events and the fact that the ammunition largely consists of iron, it is likely that the ammunition is still largely intact."
Thirty-one wrecks were possibly within 5 kilometres either side of the potential cable route and 18 of those potentially within 1 kilometre either side, the analysis said.
The wrecks' exact locations were not known.
"Of the 18 identified shipwrecks, 14 were of wooden construction and less than 500 tons, leaving one large steel vessel of 7000 tons and three of an unknown construction," it said.
"Of the 14 shipwrecks, four had an engine, meaning they could be detected by a magnetometer, as well as a side scan and multibeam sonar."
Marine geophysical data yet to be acquired would be needed for a more informed impact assessment.
Cosmos Archaeology recommended: a maritime archaeologist review marine geophysical data to identify seabed anomalies that were potentially "cultural".
They might include shipwrecks, maritime infrastructure or dump sites.
It also recommended suitably sized buffers being established to protect seabed anomalies potentially of cultural heritage significance, and removing the buffers if the anomalies were found not to be cultural or culturally significant.
Cosmos Archaeology suggested excavation might be the answer for highly significant sites if they could not be avoided.
It said the Defence Department had recorded and made available locations of sea dumping of ammunition, boats, chemical and other materials.
"However, the exact location of the dumped material may differ from that recorded due to the depth of water where the material was dumped and/or accuracy of the relocation of the dump site," the analysis said.