B and R CCD images and J NICMOS3 frames taken with the Calar Alto 3.5m telescope of the dwarf irregular galaxy UGC 685 are presented .
The brightest part of the stellar population is resolved in B and R , very few also in J .
The stellar color-magnitude diagram is discussed .
An estimate of the distance to UGC 685 of 5.5 Mpc is derived based on the brightest blue supergiant stars .
Most of the resolved bright stars show colors in the range -0.1 \leq B - R \leq + 0.7 .

The continuum light of the unresolved stars is distributed rather regular in B , R , and J , showing only minor irregularities .
This surface brightness distribution follows an exponential law in all three colors with a scale length r _ { c } = 0.33 kpc .
The central surface brightnesses are 21.57 \pm 0.09 mag / \Box ^ { \prime \prime } , 20.65 \pm 0.06 mag / \Box ^ { \prime \prime } , and 20.11 \pm 0.11 mag / \Box ^ { \prime \prime } , in B , R , and J , respectively .
The surface brightness can be traced out to 5 r _ { c } in B and R. Thus , UGC 685 belongs to the class of dwarfs where the HI distribution is much more extended ( here 2.6 times ) than the optical ( stellar ) light distribution , but contrary to many objects of this type , it does not belong to the class of low-surface brightness objects .
No color gradient was detected in UGC 685 except that the very center is slightly bluer .
The overall colors are B - R = +0.97 , B - J = +1.55 and the magnitude is B = 14.55 ( M _ { B } ^ { o } = -14.5 ) .

The classification as an irregular dwarf from survey plates results from the few HII regions of UGC 685 which are all concentrated to the South-East of the center of the galaxy .
On an H { \alpha } Calar Alto 2.2m telescope CCD image , I identified only 5 HII regions , one of them being rather bright .
The total H { \alpha } flux corresponds to a mildly on-going star formation with a rate of 0.003 M _ { \odot } yr ^ { -1 } , a low rate even in comparison to other dwarfs .
The available ( and limited ) data do not indicate any major deviation from this rather low star formation rate within the last 10 ^ { 9 } yr .