There are several jetties (see brown stripes in last map below). If all the public jetties are full a polite request to Emerald Star may enable you to moor at their jetty subject to availability.
There is always a significant stream running and it is strongly advised that mooring is executed into the stream. This is particularly true when mooring by the bridge.
DO NOT STRAY INTO THE WRONG SIDE OF THE MARKERS AT THE BRIDGE!
A list of facilities in Belturbet town is given in the Belturbet branch of IWAI web site:
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