Couple things with Bethany re: access, for those who're not familiar with it.
It's located at the intersection of NW 185th Ave and NW West Union Road, in unincorporated Washington County, just north of Hillsboro/Beaverton. The lake lies between a huge field on the south side, and a private upper-middle class neighborhood on it's north bank (with no public access on the north half of the lake.)
There is a small gravel parking lot on the west side of 185th. The other access is in a residential neighborhood, at a square dead end on NW Columbia Blvd, with only on-street parking in front of people's homes for access to the west end of the park.
A paved path stretches the length of the lake along it's south shore, there is a lot of brush along this shore, especially on the western half of the lake - and there are a few small areas that the brush has been cleared to allow anglers access to the water.
At the west end of the lake is the dam, a small low head concrete dam that lets water spill back in to Rock Creek. At the dam there is a graveled area with a picnic table and a bench - which could accomodate a few anglers.
Other users of the park include joggers, dog walkers, bicyclists, soccer players, and the occasional young man strolling through the field playing the bagpipes (I'm not kidding.)
THe south side of the field at Bethany Lake Park butts up to people's fenced back yards.
It's a nice little park - but as big as it is, it's kind of limited in the number of users thanks to parking. There's a shopping center at 185th & West Union on the northeast corner of the intersection. Westview High School is about a mile south on 185th. There is a Tri Met bus that services 185th.
The lake is a host to stocked rainbow trout, bluegill, pumpkinseed, crappie (I've caught both white & black), warmouth (very few in numbers), largemouth bass, bullhead, the oddball channel cat, along with a few different type of carp (I've caught mirror carp, common carp, and giant gold fish here before.)