I believe that the answer is number 1. Sediment is deposited as a river enters a lake because the velocity (speed) of the river decreases - the same reason that sediment gets deposited on a river's meander.
The correct answer is - (1) velocity of the river decreases.
When the velocity (the speed) of the river decreases, be it at the entry of a lake, sea, ocean, or meandering, passing through a valley with very little change in altitude, the sediment starts to get deposited. This is due to the decrease in force caused by the decrease in velocity, there is not enough force to push the sediments further so they start to deposit because the river is not able to drag them further on.
The St. Lawrence seaway helped because it was large enough to allow shipping transportation to the USA. Which allowed Canada and the USA to trade goods. The seaway extends from Montreal through the Welland Canal in Ontario, Canada, to the eastern portion of Lake Erie.
Ocean waters are salty and contain minerals and dissolved gases. They also have a high heat capacity and vary in density depending on temperature and salinity.
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of small particles and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth's surface
