Laguna de Sauce sits in a collapsed volcanic crater about an hour's drive south-east of Tarapoto, and the combination of open water, reed-fringed margins, and surrounding humid montane forest makes it genuinely productive across a full day. The lake itself is fairly shallow, which suits wading birds well, and the reeds hold skulking species that elsewhere would demand considerable patience.
You access the site via a sealed road that deteriorates toward the final stretch, so a motorbike taxi or 4WD is advisable in the wet season.
At dawn the reeds are where you want your attention. Rufescent Tiger Heron works the margins in the low light, often standing motionless close enough to study properly without optics. Azure Gallinule is present but genuinely elusive — scan the floating vegetation carefully, ideally with a scope, and accept that some visits produce nothing.
The surrounding forest edge and secondary growth reward slower walking: Large-footed Finch forages low in shaded undergrowth, and Cinereous Tinamou calls persistently at first light though locating one on the ground takes real effort and some luck.
After dark, the road between Tarapoto and the lake is well regarded for potoos. A slow drive with a good torch, stopping often, gives reasonable odds on Common Potoo perched on an exposed stub, and Andean Potoo is possible in the forest above the lake.
Local guides in Tarapoto can arrange a full day combining the lake with forest trails in the surrounding hills — worthwhile if you want serious coverage. Basic restaurants and small guesthouses operate near the lakeside, though most birders base themselves in Tarapoto.
Go between May and October to avoid the heaviest rains; bring rubber boots, a scope for the lake margins, and repellent from the moment you arrive.