[Hampshire] Ethernet connection Unscreened

I am working on a project that, at the last moment added an ethernet
connection, between two water proofed housings about 1 meter apart.
Within the boxes normal Cat 5 is used but through the housings and
connecting the two is a rather chunky specialist submarine cable which
has no shielding and no twisting of pairs. This setup scarcely works but
it does work a bit. The housings have already been manufactured and the
connection is a spare unused one which the designers thoughtfully added
but not with ethernet in mind. Should this sort of degradation be
expected? Any advice/comments would be gratefully received.

Roger