The lake covers about 26.7 hectares on the province's 1960 reconnaissance survey, which put it at a maximum depth of 11.6 m and an average of 5.1 m: a modest, shallow-leaning basin rather than a deep lake. It sits in the Columbia River watershed under waterbody identifier 00633COLR, the same drainage as Lake Enid a few kilometres northwest, near where the Columbia widens into Windermere Lake.

For an angler judging whether the drive is worth it, the release record is the honest fishing report here. Provincial hatchery records run from 1929 to 2026 and log 98 releases into Lillian Lake, all rainbow trout, totalling roughly 900,000 fish across a long list of hatchery strains: Beaver, Premier, Pennask, Gerrard Creek, Blackwater R, Fraser Valley and others, alongside the founding 1929 batch of wild-sourced Cottonwood eyed eggs.

The program has settled twice in recent decades. From 2008 to 2015 it ran as a put-grow fishery, 6,000 Blackwater R yearlings a spring. Since 2015 it has run as a put-and-take fishery instead: 2,000 Fraser Valley-strain spring catchables, stocked every April at an average weight around 225 g, sized to be caught the same season rather than grown on. The most recent plant, on 2026-04-21, followed that same pattern.

No local fishing report has turned up for Lillian Lake, so treat the following as a general read on a small put-and-take stillwater rather than a confirmed local pattern. With a shallow average depth of 5.1 m and a max of only 11.6 m, chironomids under an indicator should be productive over most of the lake through spring and into summer, since there is little truly deep water to push fish off the shoals. Standard small-lake stillwater tactics, working the shoreline and any drop-off, are the reasonable starting approach until a local report confirms otherwise.

No confirmed boat launch, road or parking details have been found for Lillian Lake. Treat it as an access-check water: confirm the road in, any private-land or seasonal restrictions, and the exact Region 4 rules that apply before committing a day to it.