Final answer:
Water's heat capacity is the property that allows it to moderate the climate around lakes by acting as a heat sink.
Step-by-step explanation:
The property of water that causes it to moderate the climate around lakes is its heat capacity. Water has a high specific heat capacity, meaning it can absorb and store a large amount of heat energy without a significant increase in temperature. This allows water bodies like lakes to act as heat sinks, regulating temperature changes in the surrounding area.
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