they slow down, release their sediment and build deltas. 水流减缓 留下大量泥沙 堆成了三角洲

229. Spectacle caiman linger below,
     眼镜凯门鳄在下面游荡
230. waiting for a meal to fall out of the sky.
     等着食物从天而降
231. When rivers finally reach the sea
     当江河最终汇入大海时
232. they slow down, release their sediment and build deltas.
     水流减缓 留下大量泥沙 堆成了三角洲
233. In Bangladesh the Ganges and Brahmaputra rivers join
     在孟加拉国 恒河与雅鲁藏布江的交汇处
234. to form the world's biggest.
     形成了世界上最大的三角洲
235. Every year almost 2 thousand million tonnes of sediment
     每年大约有20亿吨泥沙在此沉淀

来自《行星地球 第一季 第三集 Planet Earth S01E03 淡水》第 232 行