Wasn't near Lake Tahoe but a mate of mine saw something weird over Loch Lomond last month and described almost the exact same thing - silent, low altitude, lights that didn't match any aircraft pattern she's ever seen. She's ex-RAF so she's not someone who mistakes a drone for a flying saucer.
What time Thursday? And was it doing that stop-start movement thing where it just freezes mid-air for a second then carries on like nothing happened, because that seems to come up a lot with lake sightings specifically and I cannot explain why lakes seem to attract these things.
Also did you report it anywhere or just post here first? Mufon are a bit hit and miss but thier database is worth logging it on regardless.