When Spencer had secured the river boats in the harbor of San Juan he proceeded to the mouth of the San Carlos and communicated to General Mora—then at the embarcadero, some miles up the latter river—the success of the operations below. As the small steamer Spencer sent up the San Carlos approached a picket of Costa Ricans posted on a raft, the soldiers, frightened by the noise and appearance of such a boat as they had never before seen, plunged into the river and were drowned in their efforts to reach the shore. At the embarcadero Mora had, according to Costa Rican accounts, eight hundred men, with a rear guard of three hundred more expected each moment to arrive. To supply this force with subsistence six hundred men were employed in carrying provisions from the capital to the river. Much of the transportation between those points was done on the backs of men, as the trail is difficult for even mules. Castillo was forthwith occupied by the Costa Ricans; and Spencer, taking the steamer which runs over the Toro Rapids, easily succeeded, by concealing his men, in getting possession of the lake steamer, La Virgen, then lying at the mouth of the Zavalos, awaiting the return of Rogers from San Juan del Norte. Then proceeding to Fort San Carlos he lured aboard the steamer Capt. Kruger, commanding that post. The first-lieutenant of Kruger had been sent to headquarters on business connected with the garrison at San Carlos; and his second lieutenant, Tayloe, had been killed at Granada, while marching as a volunteer under Waters to the relief of Henningsen. Hence, after Kruger’s capture by Spencer, the post was in charge of a sergeant, and Kruger so far forgot his duty as to permit Spencer, under a threat of death, to extort from him an order directing the sergeant to surrender the post to the enemy. The sergeant, taken by surprise, was less to blame for obeying the order than was the captain for signing it. Thus the Costa Ricans were in possession of the San Juan river from Fort San Carlos to the sea, and they also held the smallest of the lake steamers, the La Virgen. On the latter steamer they had also taken some arms and ammunition intended for the service of Nicaragua. But the occupation of the river and the seizure of the La Virgen would have been comparatively useless to them and harmless to Walker without the capture of the steamer San Carlos. The loss of the river might have been easily repaired by the force then at Rivas, but the loss of the control over the lake was a much more serious event. Spencer well knew that he could not venture on the lake with the La Virgen as long as the larger and faster steamer remained in the hands of the Americans, and, therefore, he prevailed on Mora to keep his Costa Ricans quiet until the San Carlos got into the river with passengers from California for the Atlantic States.