The Blackwater burns green
Stannis brings the largest fleet in the realm up the Blackwater Rush and Tyrion Lannister meets it with a single chain and a great deal of wildfire. The river burns, thousands die in it, and Tywin arrives with the Tyrells at the last moment to take the credit ÔÇö and to make quite sure his son receives none of it.
The fuller tale
Stannis Baratheon brought two hundred ships and better than twenty thousand men up the Blackwater Rush to take a city held by a garrison that could not match him and a king nobody would die for. He should have won before dark.
Tyrion Lannister, acting Hand, had spent the season doing three unglamorous things: a great chain across the river mouth, wound down on a winch; the whole of the city's wildfire stock, some thousands of jars, quietly made and moved; and a plan that required letting the enemy fleet all the way in before either was used.
The river burned green from bank to bank. Ships went up with their crews aboard, men in armour went into water that was on fire, and the Blackwater ran with things that had recently been an army. Stannis landed anyway and had men on the walls, and Joffrey went inside to his mother, and it was Tyrion who put the garrison back together with a short and unheroic speech about the fact that the men outside wanted to rape their wives.
Who got the credit
Tywin Lannister arrived at the last hour with the Tyrells behind him, took Stannis in the rear, and was named Saviour of the City. Tyrion, who had a knife wound across his face and had saved it, was moved out of the Hand's chambers into a small room and given the coin.
He had held a city for a father who despised him and got nothing for it, and it is the last time he tries to earn anything from that quarter.
Elsewhere in the wiki
 See the world as it stood in 299 AC What became of it  if an ending is written, it is here. Spoilers.
The chronicle records no ending here ÔÇö or none the maesters have set down.