Liquidity Pools Explained: How AMMs Work (and the Risks)

On a traditional exchange, buyers and sellers are matched through an order book. Most decentralized exchanges work differently: they use liquidity pools and a formula called an automated market maker (AMM). If you supply crypto to a pool, you earn a share of the trading fees — but the "passive income" comes with risks that are easy to underestimate.

What a liquidity pool actually is

A liquidity pool is a smart contract holding a pair of tokens — say ETH and a stablecoin. Instead of matching individual buyers and sellers, traders swap against the pool. An AMM formula automatically sets the price based on the ratio of the two tokens in the pool: as people buy one side, it gets scarcer and pricier; the other side gets cheaper.

Anyone can become a liquidity provider (LP) by depositing an equal value of both tokens. In return you receive LP tokens representing your share of the pool.

How liquidity providers earn

Every swap pays a small fee (often around a fraction of a percent), and that fee is distributed to LPs in proportion to their share. The more trading volume a pool sees, the more fees you earn. Some protocols add extra token rewards on top — that bolted-on incentive is the heart of "yield farming," covered in yield farming risks.

So far it sounds like free money for holding tokens you already own. It isn't.

The big one: impermanent loss

Impermanent loss is the most misunderstood risk in DeFi. It happens because the AMM automatically rebalances your two tokens as their relative price changes.

In simple terms: if one token in your pair rises (or falls) sharply against the other, you end up with less of the token that gained and more of the token that lost than if you had simply held both in your wallet. The bigger the price divergence, the bigger the gap.

It's called "impermanent" because the loss only locks in when you withdraw — if prices return to where you started, it disappears. But in practice prices often don't come back, and the fees you earned may or may not make up the difference. Pairs of two closely correlated assets (like two stablecoins) have minimal impermanent loss; volatile pairs have much more.

The other risks

• Smart-contract risk. Your funds sit in code. Bugs and exploits have drained real pools. Favor audited, established protocols — and remember audits reduce risk, they don't remove it.
• Unsustainable yields. Eye-popping APYs are often propped up by token emissions that inflate away. A high headline rate frequently signals high risk, not a free lunch.
• Rug pulls and fake pools. Anyone can spin up a pool. Malicious projects create tokens, attract liquidity, then drain it. Apply the same skepticism as in avoiding crypto scams.
• Gas and complexity. Entering, exiting, and claiming rewards cost network fees, which eat into small positions. Layer 2s help here.

Is it worth it?

For some, fee income on a stable, correlated pair is a reasonable, lower-risk way to earn. For others, chasing volatile high-APY pools is closer to active speculation than passive income. The honest framing: you are taking on price risk, smart-contract risk, and complexity in exchange for fees and rewards — make sure the reward actually compensates you. None of this is financial advice, and you can lose money.

Key takeaways

• Liquidity pools let you earn trading fees by supplying a token pair to an AMM.
• Impermanent loss means you can end up worse off than simply holding, especially with volatile pairs.
• Smart-contract bugs, unsustainable emissions, and scams are real and common.
• Stable/correlated pairs are lower-risk; sky-high APYs usually mean high risk.
• Treat it as taking on risk for yield, not as free money.

New to the broader landscape? Start with what is DeFi, or compare safer earn options in crypto staking explained.